Supply to garage.

[Edward67]

Hi ok here we go.
Friend has asked if can rewire his garage as he is turning it into a gym. I said ok no problem.

He the put the spanner in. Ok I want
1 circuit for a car charger. 7.4kw.
2 x 3kw heaters
1 x ring main for gym equipment. From what i can tell running machine is most power hungry.
1 x lighting circuit.

All on a 2.5mm incoming swa.

So now I need to split the meter tails.in the cupboard and put in 25mm swa cable. Run about 12 meters.

Pme 80amp.

So looking for thoughts.

He needs cutout upgrading to 100amp. Its large 5 bed already with a hot tub.

Do you think I should install 2 core swa and TT the garage.

Or 3 core swa to mini board in meter cupboard then to isolator.
Or a two core swa with separate earth cable run next to it. This is better as earth can be smaller diameter.

Due to the size of the earthing conductor with the mini boards even accept them.

Or thinking outside the box. I could run the swa and terminate to a metal bracket mounted in the meter cupboard then run into a double isolator switch which will protect the current house tails and new swa tails.
The issue with this is the tails from the bracket to isolator are not double insulated.
However they are In cupboard that requires a key to enter so does that comply. I'm not sure.

I already know about the debated exporting pme conversation so don't wish to revisit it please.

Looking for ideas or pictures of people who have performed this.
If it wasn't for a friend I would refuse because sometimes it's best to DGI.

All comments appreciated.

Pic.of meter cupboard attached. Mmmm loads of space? think there is room for mini board.

 

[pc1966]

Or thinking outside the box. I could run the swa and terminate to a metal bracket mounted in the meter cupboard then run into a double isolator switch which will protect the current house tails and new swa tails.

An isolator won't protect the cables, it should be a fused-switch. The DNO fuse should not be relied upon for protecting your cables, it is to protect the DNO network!

That takes most space of course...

Is the car charger a smart one that monitors total load to limit the draw if one or more feed is power-constrained?
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If the gym conversion has no extraneous aspects to it then PME derived CPC presents nothing special. What you may have to consider is cable protection, and if the end Zs is low enough to meet 5s disconnection on the feed.

 

[Edward67]

An isolator won't protect the cables, it should be a fused-switch. The DNO fuse should not be relied upon for protecting your cables, it is to protect the DNO network!

That takes most space of course...

Is the car charger a smart one that monitors total load to limit the draw if one or more feed is power-constrained?
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If the gym conversion has no extraneous aspects to it then PME derived CPC presents nothing special. What you may have to consider is cable protection, and if the end Zs is low enough to meet 5s disconnection on the feed.

Hi thanks for reply.
I don't fully understand your isolator point. The current tails are 15 hence they are on the isolator seen in the picture. They do not require fused switch? So why would my swa require one.

I see your point but not entirely sure I agree otherwise all meter tails would need one wouldn't they?

Hope you respond with your thoughts.

Thankyou.

 

[pc1966]

I don't fully understand your isolator point. The current tails are 15 hence they are on the isolator seen in the picture. They do not require fused switch? So why would my swa require one.

If they are longer than 3m they should be on a fused-switch based on 433.2.2 & 434.2.1

 

[Edward67]

If they are longer than 3m they should be on a fused-switch based on 433.2.2 & 434.2.1

So does the current meb one already installed in meter cupboard comply? Regs book at work but will read those regs in morning thankyou.

 

[buzzlightyear]

1 circuit for a car charger. 7.4kw.
2 x 3kw heaters
1 x ring main for gym equipment. From what i can tell running machine is most power hungry.
1 x lighting circuit.

All on a 2.5mm incoming swa.

So now I need to split the meter tails.in the cupboard and put in 25mm swa cable. Run about 12 meters.

Do you think I should install 2 core swa and TT the garage.

You being the spark then is down to you designing it, but has for the car charger then I would go for a zappi . So you do not need to be TT unless you have water or gas services in the garage.

 

[Edward67]

You being the spark then is down to you designing it, but has for the car charger then I would go for a zappi . So you do not need to be TT unless you have water or gas services in the garage.

My idea of TT was it means no need for three core swa. Therefore I don't end up with huge 25mm earth cable in meter cupboard.

 

[davesparks]

My idea of TT was it means no need for three core swa. Therefore I don't end up with huge 25mm earth cable in meter cupboard.

Can you expand on this please because it makes absolutely no sense at the moment.

Whatever you do at the load end of the cable it must have a CPC.
Are there any extraneous conductive parts in the garage? How far is the garage seperated from the house?

Why 25mm? That seems ridiculously oversized for the loads you have described.

What type of car charger is it and will it be used indoors or outdoors? Where does it stand with regards the special regulations for car chargers?
Don't forget there is ammendment 1 which deals with car chargers.

 

[Strima]

If he needs heaters in the gym he’s not training hard enough.

 

[Edward67]

Can you expand on this please because it makes absolutely no sense at the moment.

Whatever you do at the load end of the cable it must have a CPC.
Are there any extraneous conductive parts in the garage? How far is the garage seperated from the house?

Why 25mm? That seems ridiculously oversized for the loads you have described.

What type of car charger is it and will it be used indoors or outdoors? Where does it stand with regards the special regulations for car chargers?
Don't forget there is ammendment 1 which deals with car chargers.

Obviously it needs a cpc it will be a TT?
Car charger outside and all car chargers can go on TT but not all can go on a pme due to issues with breaks in neutral conductor potentially causing the car to become live.
No extraneous conductive parts but floor is concrete therefore my understanding is it will have to be TT.
So now I have answered my own question.
I will isolate with a double isolator in the meter cupboard run to mini board in meter cupboard. Run two core swa 16mm to garage. Terminate swa in meter cupboard and earth swa. In garage I will gland the swa so it is not earthed. Then I will put in rod and run new earth to my garage consumer unit which will consist of a Type A rcd because car charger will require it and the 4 mcbs job done.

 

[R-fur]

The DNO does not normally allow customers switch gear in the meter cupboard. Why do you need another isolator in there anyway? Block the tails at the consumer unit and fit a switch fuse there for your SWA.

 

[DPG]

Obviously it needs a cpc it will be a TT?
Car charger outside and all car chargers can go on TT but not all can go on a pme due to issues with breaks in neutral conductor potentially causing the car to become live.
No extraneous conductive parts but floor is concrete therefore my understanding is it will have to be TT.
So now I have answered my own question.
I will isolate with a double isolator in the meter cupboard run to mini board in meter cupboard. Run two core swa 16mm to garage. Terminate swa in meter cupboard and earth swa. In garage I will gland the swa so it is not earthed. Then I will put in rod and run new earth to my garage consumer unit which will consist of a Type A rcd because car charger will require it and the 4 mcbs job done.

Are you going to fit a fuse before the SWA?

Edit: I misunderstood. I see you are putting a separate consumer unit on the meter cupboard??

 

[radiohead]

Henley block the tails and install an IP metal fused switch disconnector under the meter box. Tails gland into the side and SWA straight into the bottom of the FSD.
You'll struggle to get a unit in the meter box and satisfactorily terminate the SWA, aside from the fact that the supply authority don't permit it.
If you want to TT the load end then break the armouring at the garage end but use the PME for earth fault protection for the cable.

 

[davesparks]

The DNO does not normally allow customers switch gear in the meter cupboard.

The bottom right quarter of a meter box is reserved for customers equipment.

The DNO do not own the meter box, the customer does.
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No extraneous conductive parts but floor is concrete therefore my understanding is it will have to be TT.

Nonsense, having a concrete floor does not require you to install a TT system.

What changed to make you choose 16mm now? That still sounds a bit big to my mind.

So how far is the garage seperate from the house?

 

[Edward67]

The bottom right quarter of a meter box is reserved for customers equipment.

The DNO do not own the meter box, the customer does.
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Nonsense, having a concrete floor does not require you to install a TT system.

What changed to make you choose 16mm now? That still sounds a bit big to my mind.

So how far is the garage seperate from the house?

15 meters about. I understand its large but as time goes by probably not large enough when.people have two electric cars. For few pounds seems better to be safe than sorry. I changed size because 25 will be a nightmare to terminate.

 

[R-fur]

The bottom right quarter of a meter box is reserved for customers equipment. The DNO do not own the meter box, the customer does.
Source URL: Supply to garage. - https://www.electriciansforums.net/threads/supply-to-garage.188535/#post-1643781

Correct. But the supply agreement normally stipulates that the meter box is for the exclusive use of the DNO and meter operative, just the same as they always have a separate board from the consumer unit if the point of supply is inside the house.
Ownership of the meter box basically means that the customer is responsible for maintaining it.

In theory

 

[Edward67]

The bottom right quarter of a meter box is reserved for customers equipment. The DNO do not own the meter box, the customer does.
Source URL: Supply to garage. - https://www.electriciansforums.net/threads/supply-to-garage.188535/#post-1643781

Correct. But the supply agreement normally stipulates that the meter box is for the exclusive use of the DNO and meter operative, just the same as they always have a separate board from the consumer unit if the point of supply is inside the house.
Ownership of the meter box basically means that the customer is responsible for maintaining it.

In theory

I see an awful lot of consumer units in meter boxes. They never complain

 

[7029 dave]

I have been to many meter boxes , and they are jammed pack with PV equipment , isolators, switchfuse, and even seen CU's in them.(thats without the cutout)

Smart meters with comms hub and T2 Aerial if needed take up a lot of room, it would not fit with the mentioned equipment above.
It is the space for DNO and metering equipment.

 

[davesparks]

This picture from UKPNs guide for customers may help.

I believe the word contractor in the top right quarter is incorrect and should say contactor.

 

[Edward67]

Quick call the police.

Not mine btw

 

[Gavin John Hyde]

For car charger I would go for a zappi or pod point. Neither requires an earth rod but importantly both have ct clamp functions to monitor the load in the property and garage to protect the fuses. It will throttle the charger up or down according to capacity in the property. When there is little demand the charger can pull the full 32 Amps. If other things are in use it will charge at a lower rate.

 

[Edward67]

For car charger I would go for a zappi or pod point. Neither requires an earth rod but importantly both have ct clamp functions to monitor the load in the property and garage to protect the fuses. It will throttle the charger up or down according to capacity in the property. When there is little demand the charger can pull the full 32 Amps. If other things are in use it will charge at a lower rate.

Thx for advice. Sorry for slow reply.

 

[TJ Anderson]

OP, Sizing cables is down to factors other than ability to teminate!! Seriously, confirm exactly what he is having and how he will use it, then work out a realistic design current. It may save a few quid too.

 

[goasis]

This all seems a bit crazily thought out, do you always choose your cable sizes based on how easily it will be to terminate them?!

 

[TJ Anderson]

Hi thanks for reply.
I don't fully understand your isolator point. The current tails are 15 hence they are on the isolator seen in the picture. They do not require fused switch? So why would my swa require one.

I see your point but not entirely sure I agree otherwise all meter tails would need one wouldn't they?

Hope you respond with your thoughts.

Thankyou.

I just read this. I genuinely think you should decline this job.

 

[Edward67]

This all seems a bit crazily thought out, do you always choose your cable sizes based on how easily it will be to terminate them?!

No not at all. But when your only option is the meter cupboard space you start to have issues. My concern was for future car charging capacity when he has two cars but since having looked at the xlpe cable I will go for 16mm. 10mm would most probably be ok but why ---- about for 20 pound considering the 12 meters of digging.
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Nonsense, having a concrete floor does not require you to install a TT system.

Everyone is happy to criticise so I will respond. This is direct from stroma please read Dave sparks.


If the remote building has a concrete earth floor, or conductive floor, or the building is of metal construction or metal outside skin, the shock risk is increased. It’s therefore recommended that the remote building has a TT earthing system.

That is why I will TT it.

 

[TJ Anderson]

No not at all. But when your only option is the meter cupboard space you start to have issues. My concern was for future car charging capacity when he has two cars but since having looked at the xlpe cable I will go for 16mm. 10mm would most probably be ok but why ---- about for 20 pound considering the 12 meters of digging.
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Everyone is happy to criticise so I will respond. This is direct from stroma please read Dave sparks.


If the remote building has a concrete earth floor, or conductive floor, or the building is of metal construction or metal outside skin, the shock risk is increased. It’s therefore recommended that the remote building has a TT earthing system.

That is why I will TT it.

You only need to prove if it is extraneous. If it is not then you have nothing to bond.

 

[Edward67]

I just read this. I genuinely think you should decline this job.

TJ Anderson thanks for response. My response you highlighted doesn't read well. I will try to explain better for discussion. That's what it is discussion not criticism.
When meter tails are over 3m an isolator is normally needed to satisfy the dno.
If the tails were split with say swa cable and a neat way was found to terminate the swa without the need of a fused switch then what is the difference between the new swa tails and the existing house tails? If they the same rating?
The difference the swa is actually better protected than the original tails that run for 15 meters through the house.
The discussion was if the new tails absolutely have to have a fused switch then why is just an isolator acceptable for every other property in the uk with meter tails over 3m.
I will be using a fused switch, I will be changing cable size to xlpe because of its increased rating I will be TTing the system.
The reason for the TT is its safer.

I can speck the install 100 percent because he doesnt know how many chargers he wants in the future. Most probably 2 but not ruled out more.
I hold my hands up to not knowing the true capabilities of xlpe cable over standard swa but I have now been educated

Discussion forum not criticism forum. People come on for help and advice in improving installs not to be picked apart otherwise what's the point.

 

[pc1966]

The discussion was if the new tails absolutely have to have a fused switch then why is just an isolator acceptable for every other property in the uk with meter tails over 3m.

The way I have always seen the regulations interpreted is you (i.e. the designer) has to provide the switching & OCPD for cables longer than 3m.

Obviously if your cable is rated below the DNO fuse (e.g. sub-main to a garage CU in 6mm or whatever) then it is essential that you include the appropriate fuse/breaker.

Now from a simple engineering point of view there is no reason why you should add a 2nd 100A fuse immediately after the DNO fuse as you will have no selectivity. But from an ownership and legislation point of view the DNO side is separate and distinct from the installation you are designing. Theoretically they can change the ratings and/or the OCPD to suit whatever is needed for protecting their network.

So some might feel that only an isolator is needed if the long tails are adequately protected from overload by the DNO's biggest fuse option, but I have always seen it interpreted as the installation should be designed to have OCPD under your control.

 

[Edward67]

The way I have always seen the regulations interpreted is you (i.e. the designer) has to provide the switching & OCPD for cables longer than 3m.

Obviously if your cable is rated below the DNO fuse then it is essential that you include the appropriate fuse/breaker.

Now from a simple engineering point of view there is no reason why you should add a 2nd 100A fuse immediately after the DNO fuse as you will have no selectivity. But from an ownership and legislation point of view the DNO side is separate and distinct from the installation you are designing. Theoretically they can change the ratings and/or the OCPD to suit whatever is needed for protecting their network.

So some might feel that only an isolator is needed if the cables are adequately protected from overload by the DNO's biggest fuse option, but I have always seen it interpreted as the installation should be designed to have OCPD under your control.

Thankyou now that is what I call a well constructured reply. Explains the point very clearly and explains my question.

 

[TJ Anderson]

TJ Anderson thanks for response. My response you highlighted doesn't read well. I will try to explain better for discussion. That's what it is discussion not criticism.
When meter tails are over 3m an isolator is normally needed to satisfy the dno.
If the tails were split with say swa cable and a neat way was found to terminate the swa without the need of a fused switch then what is the difference between the new swa tails and the existing house tails? If they the same rating?
The difference the swa is actually better protected than the original tails that run for 15 meters through the house.
The discussion was if the new tails absolutely have to have a fused switch then why is just an isolator acceptable for every other property in the uk with meter tails over 3m.
I will be using a fused switch, I will be changing cable size to xlpe because of its increased rating I will be TTing the system.
The reason for the TT is its safer.

I can speck the install 100 percent because he doesnt know how many chargers he wants in the future. Most probably 2 but not ruled out more.
I hold my hands up to not knowing the true capabilities of xlpe cable over standard swa but I have now been educated

Discussion forum not criticism forum. People come on for help and advice in improving installs not to be picked apart otherwise what's the point.

Thank you. I apologise for my outrageous behaviour.

Absolutely......Let's continue our discussion.....

I am pleased to hear about your revelation regarding XLPE SWA. Amazing stuff it is. Can you educate me as to the equipment you are now designing to run at 90 Degrees Celsius? I have never got to do that in my limited electrical dabblings as I struggled to find suitable reasonably priced items for garages and garden shed installs etc

Why is TT safer here, we only have that PME at work. Am I in danger, I really don't understand??
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Thankyou now that is what I call a well constructured reply. Explains the point very clearly and explains my question.

Again, I'm terribly sorry and I'd like to add the irony of this was not lost on me.

 

[Edward67]

Thank you. I apologise for my outrageous behaviour.

Absolutely......Let's continue our discussion.....

I am pleased to hear to hear about your revelation regarding XLPE SWA. Can you educate me as to the equipment you are now designing to run at 90 Degrees Celsius? I have never got to do that in my limited electrical dabblings as I struggled to find suitable reasonably priced items for garages and garden shed installs etc

Why is TT safer here, we only have that PME earth thing at work. Am I in danger, I really don't understand??

A

Thank you. I apologise for my outrageous behaviour.

Absolutely......Let's continue our discussion.....

I am pleased to hear about your revelation regarding XLPE SWA. Amazing stuff it is. Can you educate me as to the equipment you are now designing to run at 90 Degrees Celsius? I have never got to do that in my limited electrical dabblings as I struggled to find suitable reasonably priced items for garages and garden shed installs etc

Why is TT safer here, we only have that PME at work. Am I in danger, I really don't understand??

Really helpful king of person. Thanks.
Two quotes. You don't know what you don't know.
And don't judge someone on their worst day to you on your best.

Now rather than criticising either help my understanding or go away. You hold the 2396 so you are perfectly capable of explaining.

I would try and explain my reasoning but sure you would just RIP it apart with no explanation.

I don't know your background and will not guess but I often find the best designers are the worst installers and the best installers are the worse designers.

Goodnight.

 

[richy3333]

For fear of this turning into a keyboard fight and getting moderated i would suggest to the OP (and am sorry if this upsets you as it is meant as positive criticism), but having read 2 pages of posts I do believe the job is beyond you; certainly from a design perspective at any rate.

Your original post details a very standard type of installation that we as sparkies often do, but your questions and comments do indicate it is something you have possibly not yet tackled before. Can you not get a more experienced contractor to let you shadow them and see how it’s done? Maybe someone from the forum can help?

 

[radiohead]

It has struck me over time on this forum that a simple supply to an outbuilding/garage/shed often seems to become a monumentally complex issue for no apparent reason.

 

[Edward67]

For fear of this turning into a keyboard fight and getting moderated i would suggest to the OP (and am sorry if this upsets you as it is meant as positive criticism), but having read 2 pages of posts I do believe the job is beyond you; certainly from a design perspective at any rate.

Your original post details a very standard type of installation that we as sparkies often do, but your questions and comments do indicate it is something you have possibly not yet tackled before. Can you not get a more experienced contractor to let you shadow them and see how it’s done? Maybe someone from the forum can help?

Was having bad day yesterday. Little.one went to hospital with peanut reaction so will take it o the chin.
Mr TJAnderson has opened my eyes to looking at it from a different perspective and he is entirely correct in his xlpe comment on cable selection.
I have got another very experienced contractor to aid in this but wanted to explore all options in open environment.
I think the forum would a better place if instead of people just saying why or wouldn't do that they explain their own view and reasoning as in with pme. Which has been discussed numerous times on many forums and always results in differing opinions.
Any more information on exporting pme that is concrete and not a personal view would be appreciated.

 

[7029 dave]

It has struck me over time on this forum that a simple supply to an outbuilding/garage/shed often seems to become a monumentally complex issue for no apparent reason.

Might have something to do with special locations

 

[pc1966]

Also it is not a "standard circuit" that you can just look in the OSG table for a yes/no based on load, length and CSA.

There is the special location side - the whole CPC from PME in another location with or without extraneous conductive parts bonding to worry about.

Then you have the simple circuit, say a couple of sockets and FCU for lights fed from house CU slot, versus a sub-main to a 2nd CU/DB and the whole OCPD/RCD selectivity arguments that go with planning that.

 

[richy3333]

@Edward67 hope the little dude is ok, really worrying when as a dad you can’t fix it and have to trust others.

The forum works best (imho) when someone says whom they are, their experience and then ask for help, having shown their calculations and described what they are to achieve or drawn a diagram etc. Part of the problem is that there are too many DIYers on here pretending to know something when they clearly don’t (I’m in no way suggesting that’s you).

I hope you keep posting questions ?

 

[Edward67]

@Edward67 hope the little dude is ok, really worrying when as a dad you can’t fix it and have to trust others.

The forum works best (imho) when someone says whom they are, their experience and then ask for help, having shown their calculations and described what they are to achieve or drawn a diagram etc. Part of the problem is that there are too many DIYers on here pretending to know something when they clearly don’t (I’m in no way suggesting that’s you).

I hope you keep posting questions ?

Ok will attempt to post with more depth in future.

 

[radiohead]

Any more information on exporting pme that is concrete and not a personal view would be appreciated.

You are not 'exporting PME', you are simply extending an existing earthing system.
I've never ever heard anyone say they are 'exporting TNS....or TT'.

Might have something to do with special locations

It's not a special location.