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Hello all

A quick question about an existing layout if I may.

The layout consists of a main CU connected to a sub panel via a single 63 amp MCB.

A Dorman Smith K1PC63 to be exact.

Total potential load on the sub panel is 25Kw.

Routinely all of that load is present on the sub panel throughout the day apart from two dishwashers (10 Kw) which are in service for about 25% of the time.

What do you think about that MCB? Underrated given the load or adequate?

I have my own opinion which is it should be considerably higher. Also, possibly, the cable that connects the two but I don't know about that because I haven't looked at it.

But I would like to hear your opinions if that's ok.

Cheers.
 
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SparkyChick

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Is the MCB tripping? Any signs of thermal damage? Have you clamped the cable to get an idea of actual current flow?

Sounds like a kitchen, in which case diversity may apply to a lot of the 25kW. The two dishwashers won't be pulling 5kW each all the time they are on, much of that is likely to be the wash water heating which will cycle reducing the overall load, depending on size, it could well be just a few hundred watts for control and pump power.

A full list of appliances and their loads may help provide a better answer, but if it's not tripping, there's no evidence of thermal damage to the cable or breaker, I'd be inclined to leave well alone pending a better assessment of the actual current that is likely to be flowing.
 
D

Deleted member 26818

From what the OP says, 75% of the time, the board is running at or close to the max.
For the 25% of the time, the board is running at or close to 1.6 x max.
Is this 3 phase, single phase or a mix of both?
 
  • Thread Starter Thread Starter
  • #5
Have you measured the actual current drawn from the Sub Panel?
No. I am acting in an advisory capacity so I won't be touching anything or opening up the CU or sub panel.
 
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  • #6
From what the OP says, 75% of the time, the board is running at or close to the max.
For the 25% of the time, the board is running at or close to 1.6 x max.
Is this 3 phase, single phase or a mix of both?
Yes. That's my concern. I feel it should be a 125 amp to limit it to about 80% of capacity.
 

darkwood

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I wouldn't be feeding a sub-main via an mcb anyway, it is poor design from the off unless the distribution of the sub-main are rated low enough to give the discrimination that should be factored into design.

If this is indeed wrong due to demand then as long as the cable is rated higher than the mcb after all factors applied then at least it is not an immediate fire risk, this of course do not mean it is correct.

From the info you provide it is likely the mcb is experiencing small overloads for extended periods of time which is definately a worry, if it was getting large overloads then it would be nuisance tripping but that has not been disclosed here so assume it isn't.
 
  • Thread Starter Thread Starter
  • #8
I wouldn't be feeding a sub-main via an mcb anyway, it is poor design from the off unless the distribution of the sub-main are rated low enough to give the discrimination that should be factored into design.

If this is indeed wrong due to demand then as long as the cable is rated higher than the mcb after all factors applied then at least it is not an immediate fire risk, this of course do not mean it is correct.

From the info you provide it is likely the mcb is experiencing small overloads for extended periods of time which is definately a worry, if it was getting large overloads then it would be nuisance tripping but that has not been disclosed here so assume it isn't.
I concur. The puzzlement here is that this was all installed from scratch in a new building by a qualified electrician, part of a project team, who had access to layout drawings and a complete inventory of all equipment that would require electricity so the is no question that the full potential load was calculable. So why would he choose a 63 amp MCB under thos circumstances irrespective of whether a sub panel is teh best approach. And if he was happy to underrate that then it's not inconceivable he might apply the same policy to the cabling. That's wher it becomes problematic because it's one thing to upgrade the MCB but it's ane entirel different prospect when it comes to the cable. It's all buried too so it's teh worse case scenario from an overheating perspective.

There is a lot of other stuff as well with this installation. Most of the MCBs are the wrong way round in CU. Off is on and on is off. I know it doesn't make any difference functionally but you intuitively expect Green to indicate ON and Red OFF not the other way round. Confusing when you are looking for a tripped switch. To me that's just laziness.
 
D

Deleted member 26818

It is a poor design, no two ways about it.
Before making any decision about increasing the rating of the MCB, you should first establish the rating of the cable supplying the board.
I would also want to know what temperatures the MCB is running at, so as to consider what effect it is having on adjacent MCBs.
 
  • Thread Starter Thread Starter
  • #10
It is a poor design, no two ways about it.
Before making any decision about increasing the rating of the MCB, you should first establish the rating of the cable supplying the board.
I would also want to know what temperatures the MCB is running at, so as to consider what effect it is having on adjacent MCBs.
Yes. As I have just replied to darkwood. The feedback so far from you guys suggests the way forward is to recommend a full inspection of the cable that connects the CU and sub panel with a proposal to increase the capacity from 63 amps to 125 amps (my estimation) whatever that involves. Thanks.
 

darkwood

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You say as part of a project team and also use the term Qualified Electrician too...

Was this a skills course teaching practical skills that should have been overseen by a competent person?

The term Qualified Electrician means nothing on its own, competent is the term one is looking for nowadays.

I personally wouldn't worry if the cable does need replacing either, you are not the designer or installer of this mess you are merely passing on your concerns and possible remedies to resolve them, if it does indeed need digging up then that will fall on the original designer and/or installer.
 
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  • #12
It is a poor design, no two ways about it.
Before making any decision about increasing the rating of the MCB, you should first establish the rating of the cable supplying the board.
I would also want to know what temperatures the MCB is running at, so as to consider what effect it is having on adjacent MCBs.
I am actually looking to see if I can get hold of an IR camera so I can see it there are any hot spots on the panels or the walls where the trunking runs.
 

darkwood

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I am actually looking to see if I can get hold of an IR camera so I can see it there are any hot spots on the panels or the walls where the trunking runs.
Use the palm of your hand, its cheaper and instant results, the issue is any heat build up may not be constant but intermittent and it may come down to the fact you check it at the wrong time to get any real feedback..

Just look at the cable terminations, gauge its size and calculate its suitability for the job with all cable factors included, you need not go into testing or the like to establish this is a poor/dangerous install.
 

Andy78

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Yep, an awful design in all respects.
As to the why a 63A MCB was chosen I think this might be quite simple. It is clear that the person installing did not quite know what they were doing. They have determined for whatever misguided reason that a standard TPN board was sufficient to feed this distribution circuit. A standard TPN board usually has a maximum of 63A devices. I know some ranges go above this but I'm talking in general, I don't really know the Dorman Smith ranges.

If your capacity is only advisory I would advise a data logging exercise to ascertain the real usage of the circuit.
 
  • Thread Starter Thread Starter
  • #16
You say as part of a project team and also use the term Qualified Electrician too...

Was this a skills course teaching practical skills that should have been overseen by a competent person?

The term Qualified Electrician means nothing on its own, competent is the term one is looking for nowadays.

I personally wouldn't worry if the cable does need replacing either, you are not the designer or installer of this mess you are merely passing on your concerns and possible remedies to resolve them, if it does indeed need digging up then that will fall on the original designer and/or installer.

I don't know. It was a new build and managed by external project manaf=ge
Use the palm of your hand, its cheaper and instant results, the issue is any heat build up may not be constant but intermittent and it may come down to the fact you check it at the wrong time to get any real feedback..

Just look at the cable terminations, gauge its size and calculate its suitability for the job with all cable factors included, you need not go into testing or the like to establish this is a poor/dangerous install.

Ok. Cheers. BTW what's the normal life expectancy of these MCBs. These have been in service for just over 4 years. Reason I ask is because one of the wall sockets on a circuit off the main CU overheated and actually melted and I would have thought the associated MCB would trip before it got to that point. It didn't. So I am wondering whether to recommend replacing at least the ones I suspect might be malfuntioning. That's another issue with this install. It is very difficult not to overload the socket curcuits off the main CU. There are 16 x 13 amp outlets and only 3 x 32 amp MCBs. Total potential load is 208 amps. Like I said. Bewildering.
 
  • Thread Starter Thread Starter
  • #17
Yep, an awful design in all respects.
As to the why a 63A MCB was chosen I think this might be quite simple. It is clear that the person installing did not quite know what they were doing. They have determined for whatever misguided reason that a standard TPN board was sufficient to feed this distribution circuit. A standard TPN board usually has a maximum of 63A devices. I know some ranges go above this but I'm talking in general, I don't really know the Dorman Smith ranges.

If your capacity is only advisory I would advise a data logging exercise to ascertain the real usage of the circuit.
Thanks. I will make a note of that.
 
  • Thread Starter Thread Starter
  • #19
It is a poor design, no two ways about it.
Before making any decision about increasing the rating of the MCB, you should first establish the rating of the cable supplying the board.
I would also want to know what temperatures the MCB is running at, so as to consider what effect it is having on adjacent MCBs.
Thanks for your input. will go back and try that.
 
  • Thread Starter Thread Starter
  • #20
Yep, an awful design in all respects.
As to the why a 63A MCB was chosen I think this might be quite simple. It is clear that the person installing did not quite know what they were doing. They have determined for whatever misguided reason that a standard TPN board was sufficient to feed this distribution circuit. A standard TPN board usually has a maximum of 63A devices. I know some ranges go above this but I'm talking in general, I don't really know the Dorman Smith ranges.

If your capacity is only advisory I would advise a data logging exercise to ascertain the real usage of the circuit.
Thanks. A few of you have suggested that so it's on the to do list.
 
  • Thread Starter Thread Starter
  • #21
Is the MCB tripping? Any signs of thermal damage? Have you clamped the cable to get an idea of actual current flow?

Sounds like a kitchen, in which case diversity may apply to a lot of the 25kW. The two dishwashers won't be pulling 5kW each all the time they are on, much of that is likely to be the wash water heating which will cycle reducing the overall load, depending on size, it could well be just a few hundred watts for control and pump power.

A full list of appliances and their loads may help provide a better answer, but if it's not tripping, there's no evidence of thermal damage to the cable or breaker, I'd be inclined to leave well alone pending a better assessment of the actual current that is likely to be flowing.
Not on the sub panel circuitry. But on the main CU circuitry. Melted socket internally but no tripping of MCB which is odd. I suspect the MCB may be faulty so you can't take it for granted that there is no tripping. It's a busy cafe. But even without the dishwashers the MCB is at full capacity. I don't know about the cable. Other have sugested data logging exercise so that would appear to be the next logical step.
 
T

Toneyz

I am a bit surprised that the kitchen was not a 3 phase supply and the load balanced as best as practical.
 

darkwood

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MCB's detect current overload and short circuit, a loose connection overheating will not be seen by the mcb (unless it damages the cable or socket enough it shorts out), I really think this install needs a detailed test and inspection as it sounds like you have a list of issues and concerns here.
With a full electrical report you can then approach the original contractor and present your concerns and a good case if the report reveals anything.
 

Pete999

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MCB's detect current overload and short circuit, a loose connection overheating will not be seen by the mcb (unless it damages the cable or socket enough it shorts out), I really think this install needs a detailed test and inspection as it sounds like you have a list of issues and concerns here.
With a full electrical report you can then approach the original contractor and present your concerns and a good case if the report reveals anything.
Absolutely.
 
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  • #25
MCB's detect current overload and short circuit, a loose connection overheating will not be seen by the mcb (unless it damages the cable or socket enough it shorts out), I really think this install needs a detailed test and inspection as it sounds like you have a list of issues and concerns here.
With a full electrical report you can then approach the original contractor and present your concerns and a good case if the report reveals anything.
That's reasonable. I believe I have enough ammo to make that recommendation but I think the conclusions will be much the same as mine ie: it needs changing. Sooner rather than later. It's just a matter of defining the scope.
 
I am a bit lost with this. You have been asked to look at a situation in an advisory capacity but you come on an internet forum asking advice which says to me you don't have the necessary knowledge or experience to give advice?
 
D

Deleted member 26818

I am a bit lost with this. You have been asked to look at a situation in an advisory capacity but you come on an internet forum asking advice which says to me you don't have the necessary knowledge or experience to give advice?
He’s just getting second opinions.
 

davesparks

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It is very difficult not to overload the socket curcuits off the main CU. There are 16 x 13 amp outlets and only 3 x 32 amp MCBs. Total potential load is 208 amps. Like I said. Bewildering.
Are these general use sockets or are they intended for specific appliances?

16x 13A outlets spread across 3x 32A ring circuits seems well provisioned for general use outlets
 
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  • #29
I am a bit lost with this. You have been asked to look at a situation in an advisory capacity but you come on an internet forum asking advice which says to me you don't have the necessary knowledge or experience to give advice?
I have plenty of knowledge and experience. It's called "seeking a second opinion". The reason I have come here is because I am bewildered at what I am seeing given that it was designed and installed by someone who you would probably be happy to describe as having the "necessary knowledge and experience". Everything I see is way beyond the boundaries of what I would expect from someone with the "necessary knowledge and experience" required to install safe systems. So, I have come here to see if there are others on here who find this as alarming as I do. That would appear to be the case and I am grateful for their indulgence.
 
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  • #31
Are these general use sockets or are they intended for specific appliances?

16x 13A outlets spread across 3x 32A ring circuits seems well provisioned for general use outlets
They are all general sockets. 8 x 2 port 13 amp. But it's more to do with the layout. The list of equipment detailed 4 main items along with a few other peripheral devices. A grill and three hotplates. A total of 50 amps for those items alone. I would have liked to see dedicated outlets for these 4 devices with their own single 64 amp MCB and circuit. At this point in time there is nothing to stop someone plugging 8 x 13 amp devices into one of these segments while it only has a 32 amp MCB. You can't expect the end user to know the dangers of doing so. The layout should be designed to prevent it in my opinion. As far as is reasonably possible at least. If you tskr this to its extreme it is possible to demand 208 amps from the CU through three segments each with a 32 amp MCB.
 

SparkyChick

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It is not possible to demand 208 amps from the CU... if this is the sub-board, it's protected by a 63A MCB which will allow a small overload for some time, but not a significant one, and if it's all on one phase (the fact the MCB is a single phase unit - unless the model number is wrong), unless it's a 200A supply, I would expect the suppliers fuse to rupture.

So why is this being investigated now? What reason has the business had to get so concerned?
 
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  • #33
It is not possible to demand 208 amps from the CU... if this is the sub-board, it's protected by a 63A MCB which will allow a small overload for some time, but not a significant one, and if it's all on one phase (the fact the MCB is a single phase unit - unless the model number is wrong), unless it's a 200A supply, I would expect the suppliers fuse to rupture.

So why is this being investigated now? What reason has the business had to get so concerned?
Trippings and internally melted sockets. All equipment recently PAT tested and deemed fit for purpose.
 

SparkyChick

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Is it the 63A MCB supplying the sub-board? If so, how long has it been going on? I ask how long because if it's significantly less than 4 years one might assume that something has changed. If it's not that MCB, what is supplied by the MCB(s) that trip?

As for the melted sockets, that's not an indicator the design is bad... could be a loose connection in the plug, loose fuseholder, cheap socket outlet, substandard fitted plug (on a piece of cheap equipment maybe). There are plenty of reasons a plug can melt that are nothing to do with the design.
 
We used to do a lot in fast food restaurant kitchens and there was a practice of multiple radial circuits to single point sockets. The layout was often mirrored especially the drive-through outlets and a socket served a particular piece of equipment and it had nothing to do with the current load of the equipment. The chain of thought was losing a multiple outlet radial or ring final through whatever reason meant the loss of several items of equipment and possible closure of the outlet. Lose a single point radial was not likely to prevent trading.
 
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  • #36
It is not possible to demand 208 amps from the CU... if this is the sub-board, it's protected by a 63A MCB which will allow a small overload for some time, but not a significant one, and if it's all on one phase (the fact the MCB is a single phase unit - unless the model number is wrong), unless it's a 200A supply, I would expect the suppliers fuse to rupture.

So why is this being investigated now? What reason has the business had to get so concerned?
I'm not sure what you mean by "not possible to demand 208 amps". If I walk in there now and plug a 3Kw kettle into each of the 16 outlets and switch them on what do you suggest would happen?
 
T

Toneyz

We used to do a lot in fast food restaurant kitchens and there was a practice of multiple radial circuits to single point sockets. The layout was often mirrored especially the drive-through outlets and a socket served a particular piece of equipment and it had nothing to do with the current load of the equipment. The chain of thought was losing a multiple outlet radial or ring final through whatever reason meant the loss of several items of equipment and possible closure of the outlet. Lose a single point radial was not likely to prevent trading.
I would have thought that this would have been a more suitable design.
 
T

Toneyz

I'm not sure what you mean by "not possible to demand 208 amps". If I walk in there now and plug a 3Kw kettle into each of the 16 outlets and switch them on what do you suggest would happen?
But that would not happen in the real world. Have you got a list of equipment that they are using?
 

SparkyChick

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I'm not sure what you mean by "not possible to demand 208 amps". If I walk in there now and plug a 3Kw kettle into each of the 16 outlets and switch them on what do you suggest would happen?
I would expect the OCPDs protecting the circuit or if this on the sub-board (protected by a 63A MCB) to trip at the very least, and unless the suppliers OCPD is over 100A, I'd expect that to rupture.
 
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  • #40
But that would not happen in the real world. Have you got a list of equipment that they are using?
I doubt you would get away with that excuse if you found yourself on the end of a corporate manslaughter charge through negligence. The way I see it is this. You can't do a great deal with existing layouts other than enhance and improve. But when you start off with a blank sheet it should never be possible at sign off for the end user to demand more from the system than it is capable of supplying. That's the whole purpose of the legislation. You start off with a list of the demands that need to be catered for safely at the outset. Then you can discuss issues of scalability with the client. For example you might only need 3 hotplates today. Tomorrow you might need 6 if business goes well. So you design for expansion if that arises. Whatever the total demand is then that's what the supply should be capable of delivering. Ideally at 80% capacity. Certainly not 50% less.
 

SparkyChick

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Unfortunately, in reality, it's almost always possible for an end user to demand more than their supply is capable of handling, which is why OCPDs are installed. Take a look around your home and ask yourself what would happen if I plugged a 3kW kettle into every socket in my kitchen.

The OCPDs in the board are there to protect the installation wiring and little else and the suppliers OCPD is there to ensure the install as a whole doesn't exceed it's capabilities.

But it's still not clear what's tripping, and when the tripping started. You're just basically pointing the finger at the spark who you've been told designed and installed this 4 years ago, so I'll say this... if these tripping problems were not present when the installation was signed off 4 years ago (if they were, they should have been reported to the original contractor), and only started in say the last 18 months or so I'd suggest the client has changed something and introduced equipment that pushes the demand beyond the capabilities of the installation (as designed 4 years ago based on the information available to the spark at the time).

I actively try and encourage my clients to include some additional capacity 'for the future' but there comes a point where it's not practicable or financially viable. If it was a new business, they possibly had budget constraints so the spark may have been financially impeded. There's so many factors that could have played a part in his decision making process and you can pretty much guarantee you won't get the negative points from the client since they obviously want you on their side.
 
Unless I have missed it SC there is no mention of tripping circuits so I am still confused what he has been asked to advise on.
 
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  • #46
Sorry don't get that.
The calculations based on projected demand vs the limitations actually implemented by the solution which appear to fall short of what is required in this case. Somebody used the term "likely" earlier on. That's a term used when referring to chance and probability. I don't believe anything should be left to chance where safety is concerned. Demand is easily definable and providing a delivery mechanism that meets the demand is also straight forward. There's no reason why chance should play a part. The numbers in this case don't line up. Too much left to chance. Alarmingly so.
 
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  • Thread Starter Thread Starter
  • #49
Unfortunately, in reality, it's almost always possible for an end user to demand more than their supply is capable of handling, which is why OCPDs are installed. Take a look around your home and ask yourself what would happen if I plugged a 3kW kettle into every socket in my kitchen.

The OCPDs in the board are there to protect the installation wiring and little else and the suppliers OCPD is there to ensure the install as a whole doesn't exceed it's capabilities.

But it's still not clear what's tripping, and when the tripping started. You're just basically pointing the finger at the spark who you've been told designed and installed this 4 years ago, so I'll say this... if these tripping problems were not present when the installation was signed off 4 years ago (if they were, they should have been reported to the original contractor), and only started in say the last 18 months or so I'd suggest the client has changed something and introduced equipment that pushes the demand beyond the capabilities of the installation (as designed 4 years ago based on the information available to the spark at the time).

I actively try and encourage my clients to include some additional capacity 'for the future' but there comes a point where it's not practicable or financially viable. If it was a new business, they possibly had budget constraints so the spark may have been financially impeded. There's so many factors that could have played a part in his decision making process and you can pretty much guarantee you won't get the negative points from the client since they obviously want you on their side.
Maybe I'm splitting hairs here but it IS possible to demand the resources. But what you are sdaying it's not possible to deliver it because the OCPDs will prevent it from being delivered. Yes. I know. But its better, in my opinion, if you can design the layout so that the demand doesn't outreach the supply. That's also possible.
 
The calculations based on projected demand vs the limitations actually implemented by the solution which appear to fall short of what is required in this case. Somebody used the term "likely" earlier on. That's a term used when referring to chance and probability. I don't believe anything should be left to chance where safety is concerned. Demand is easily definable and providing a delivery mechanism that meets the demand is also straight forward. There's no reason why chance should play a part. The numbers in this case don't line up. Too much left to chance. Alarmingly so.
There you go then the system was badly designed for its intended purpose. State your findings in a Report and job done.
 
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  • #51
Ok. Thanks to everyone for their input. I have what I wanted from this post. That's great. I appreciate it. Just to be clear. When I posted this it was because I was looking for opinion more so than advice. I know that there is something not right about this setup. I knew it when I started listing the devices and looking at the layout. I am alarmed by what the numbers revealed. But I am very particular when it comes to theory and best practice. I appreciate that not everyone is as pernickety as I am and what I wanted to do was get a feel of how others would approach this situation. What I have found is that there seems to be a mixture of feedback. Some find these numbers as concerning as I do, others seem to be happy to leave it to chance and other still don't actually see a problem. I will take the data logging suggestion forward. That seems like a good idea and straight forward enough. But there will be changes recommened to the supply layout in the interest of safety. That is for sure. I think it would be remiss of me not to do so. Thanks again.
 

Andy78

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I'd say if the numbers that alarm you are based on your earlier allowance of 13A per 13A outlet, then that assertion is the problem with the numbers.
 

SparkyChick

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I'm guessing I fit into the leave it to chance or the don't see a problem category and if that's your opinion, you've failed to understand my line of questioning.

You still haven't answer what I consider to be fundamental questions... when did this tripping issue start? and what is actually tripping and when?

You've not provided a complete breakdown (per item) of equipment and you personally have no way of knowing whether it is the same list that was supplied to the original spark. A complete breakdown would allow a proper assessment of diversity (which in case you're not aware Ray is the method by which we regularly undersize supplies).

Why I'm challenging this is because as per bloody usual, there's a significant amount of 'must be the sparks fault', 'poor design' without actually knowing the full story. Melted plugs and sockets does not necessarily equal poor design... poor quality accessories, poor terminations maybe but it definitely doesn't automatically mean poor design.
 

SparkyChick

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And another side step of my question.

If you go in all guns blazing making statements the installation is not up to scratch it could have serious ramifications for someone's business. Do I think there are some not so good decisions based on what you've said... yes. Do I think there could be mitigating circumstances... maybe. New install for a new business, possibly budgetary constraints and he did the best he could? Who knows. Certainly none of us do.

If this tripping is a recent turn of events, you should perhaps proceed on the basis that things have changed, probably around the time the tripping started.

Could be the installation was perfectly good for what was there 4 years ago, but isn't up to the demands of the business now.
 
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  • #56
And another side step of my question.

If you go in all guns blazing making statements the installation is not up to scratch it could have serious ramifications for someone's business. Do I think there are some not so good decisions based on what you've said... yes. Do I think there could be mitigating circumstances... maybe. New install for a new business, possibly budgetary constraints and he did the best he could? Who knows. Certainly none of us do.

If this tripping is a recent turn of events, you should perhaps proceed on the basis that things have changed, probably around the time the tripping started.

Could be the installation was perfectly good for what was there 4 years ago, but isn't up to the demands of the business now.
As I said ealier this posting was not smuch a plea for advise or diagnosis. It was a straw poll on my interpretation of the findings. It appears opinions vary which is fine. Thanks for your input.
 
T

Toneyz

I am in agreement with Sparkychicks reply(s)
we have both asked regarding the equipment that is being used.
I think we are all in agreement that a load logger would be a great
source of providing load information.
You keep on saying "numbers" what numbers?
There should be an O&M manual with "as fitted" drawings this may show what was designed for then and could show what load has been added.
The burnt out plug and sockets would probably down to poor contact did the equipment come with a moulded plug or has this been added to something that was designed to be hard wired on a dedicated circuit.
What effect is this load having on the 3 phase supply and is it maybe overloading one of the phases on the D.B?
 

TJ Anderson

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As I said ealier this posting was not smuch a plea for advise or diagnosis. It was a straw poll on my interpretation of the findings. It appears opinions vary which is fine. Thanks for your input.
Blown away by this post.

Sound out of your depth mate tbh.

Confirm if Iz>In for that 63A sub then forget about it for now.

You've got 13A sockets melted and your worrying about the OCPD upstream of the one protecting the circuit in question.

Also, diversity......wtf......you've got the actual install in front of you. You need to get a clamp meter out.

Probably nothing more than 3kW appliances plugged into sockets running for long durations.
 
As others have now said, you don't seem to have any awareness of diversity and how it is applied. Taking your example of plugging a 3kw kettle into each outlet, you wouldnt be able to turn them all on at once, empty them and refill them all at once, and turn them back on again. So even if you were making 500 hot drinks, its likely only 3 or 4 would be on at once, as the others would be being used/refilled. This principal is applied to most electrical loads in some way, especially heating loads controlled by a thermostat, which can be cycled.

It does sound like more capacity is now needed in your installation, but until you find the actual numbers for what is being used, and how and when, you wont know this for certain.

As for the safety aspect, running an installation constamtly at 100-120 percent of its capacity will significantlt shorten its life, and if this is the case it needs to be upgraded. But as mentioned, providing the OPCDs are correctly sized for the cable they will operate before the cables overheat.

And to give you an idea of how diversity is applied, i believe the national grid used to allow for 1kw per house (it may be slightly higher than this now but i dont think by much)
 
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  • #60
Sound out of your depth mate tbh.
Actually, I was thinking exactly the same thing about the guy who implemented this crap. MCBs the wrong way round etc. Different folks have different standards I guess.
 

darkwood

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Actually, I was thinking exactly the same thing about the guy who implemented this crap. MCBs the wrong way round etc. Different folks have different standards I guess.
With the questioning and extra information you have supplied after my earlier comments, it has become clear you are out of your depth here, you are taking on an advisory role without the knowledge to give an informed opinion, the fact we have had to explain what I would class as basic electrical knowledge for anyone in your position is somewhat disturbing, my original help was given as I thought you were in a position of say a maintenance person with a keen interest etc without any formal training hence my advice to get an inspection done, as it has become clear you have been called in to assess and report on this installation yet lack basic understanding of even the operation of an MCB then I can only come to the conclusion that this thread needs closing and you need to get a competent knowledged person in... you have provided enough responses in my mind to establish you are not competent.

Thread closed.
 
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