Electric connections to outbuildings

[Deleted member 73437]

Hello,
I would begrateful for some advice.
I have recently moved into a property which has two detached outbuildings, one used as a garage and the other as a workshop, no heavy machinery just the run of the mill drills and saw.

The outbuildings are connected to the house in this manner;
From main ConsumerUnit, 80A / 30mA RCD via a 32A MCB to the Garage Consumer Unit,63A / 30mA RCDvia a 32A MCB to the Workshop Consumer Unit, 40A / 30mA RCD. The circuit is earthed via an earth rod ouside the house.

What I would like to know is does this meet the existing requirements or is it an overkill?

I am not after technical details as I intend to contact a local electrician. What I will be grateful for is some information, if this set up does not meet standards, so that I can have an idea for when I get the quotes.

Kindregards

 

[GLENNSPARK]

cant see an issue here...

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depends on the CSA of the supply cable....you may be able to up the MCB top end....

 

[GLENNSPARK]

just a thought....is the supply cable here an SWA?...if so then go for an 100mA s type RCD top end with your finals given fault protection by 30mA RCDs (which you already have there)...so as to avoid the discrimination issues with RCDs of the same type in series

 

[Richard Burns]

Yes you seem to have three 30mA RCDs in series which is pointless, but it is possible that each RCD is not in series depending on how each CU is wired.
You also have two 32A MCBs in series which provide no discrimination.
The discrimination issues would be technically a breach of the regulations if there is danger from the power outage of the entire run because of a fault at the end of the run, but this would likely not be the case in a domestic situation.
Other than that then as Glennspark says above.

 

[Deleted member 73437]

I am very grateful for your responses.

The cable from the house to the garage and the workshop is 10mm twin and earth which is housed in a very tough plastic conduit and runs above ground fixed to the walls.

Glennspark do you mean change the 80A RCDin the house consumer unit to a 100A?

Also, will it help to have an earth rod fitted to each of the consumer units?

Once again,many thanks

 

[telectrix]

Glennspark do you mean change the 80A RCDin the house consumer unit to a 100A?

no , he means the 32A MCB. feeding the 10mm. this can be uprated to a 40A, what is the present earthing system?

 

[Deleted member 73437]

Glennspark do you mean change the 80A RCDin the house consumer unit to a 100A?

no , he means the 32A MCB. feeding the 10mm. this can be uprated to a 40A, what is the present earthing system?

The earth is through an earth rod just outside the house

 

[telectrix]

then adding extra rods might be advantageous. what's the Ze

edit: sorry, just re-read yor OP. get your local spark to work everything out for you.

 

[Deleted member 73437]

then adding extra rods might be advantageous. what's the Ze

edit: sorry, just re-read yor OP. get your local spark to work everything out for you.

Manythanks, I do intend to get a local electrician to carry out an inspection ofthe whole system, in fact I have been phoning around this morning. I just wouldlike some ideas before I am baffled with science and fobbed off with a totalrewire or something.

From thereplies, I assume overall the system is fine bar from needing some tweaking toimprove the overall safety.

 

[telectrix]

if the installation is post 1980, then it should be fine. as you say, maybe a bit of updating required. be aware though, that many installations will not comply fully with current regs. that does not mean that they have to be updated. it's new work that has to be installed to latest regs.. earthing and bonding arrangements need to be inspected and if not adequate, will need upgrading.

 

[Deleted member 73437]

if the installation is post 1980, then it should be fine. as you say, maybe a bit of updating required. be aware though, that many installations will not comply fully with current regs. that does not mean that they have to be updated. it's new work that has to be installed to latest regs.. earthing and bonding arrangements need to be inspected and if not adequate, will need upgrading.

Yes the installation is post 1980, it was done as part of house extension. Thanks for clarifying the current situation. Already, one electrician I spoken to over the phone has suggested that the system does not seem to meet the new regs and therefore any works would be classed as ¨new works¨therefore the whole system might need to be changed. This is what I am trying to avoid, hence my seeking advice.
The first electrician who responds in the same vein as you kind folk will get the job. Many thanks again.

 

[telectrix]

i'm sure there are a few forum members in your area. look on the electricians in your area forum, or post a thread inj the general forum, titled " electrician wanted, ipswich"

edit: you're a bit outside my catchement area .LOL.

 

[Engineer54]

Take a few photo's of your 3 X consumer units, preferably with the covers removed so that we can see what you actually have. We can then recommend the best way to go ahead with as to, what to ask the electrician to quote against...

I would however recommend, that you do install an earth rod (2 X 5/8'' coupled together for depth) at each of the 2 outbuildings as a matter of course. Connecting these 2 additional rods with the house's main rod will not only serve the two outbuildings, but also lower the overall Ra value, which serves the main house installation too!!

 

[GLENNSPARK]

Take a few photo's of your 3 X consumer units, preferably with the covers removed so that we can see what you actually have. We can then recommend the best way to go ahead with as to, what to ask the electrician to quote against...

I would however recommend, that you do install an earth rod (2 X 5/8'' coupled together for depth) at each of the 2 outbuildings as a matter of course. Connecting these 2 additional rods with the house's main rod will not only serve the two outbuildings, but also lower the overall Ra value, which serves the main house installation too!!

yeah....caus you just know it`l be a 3/8" stalk....doin nowt....lol...

 

[telectrix]

if you can manage to get a rod through the foul drains, the Ra should become good every time the bog gets flushed. :ciappa:

 

[Deleted member 73437]

Take a few photo's of your 3 X consumer units, preferably with the covers removed so that we can see what you actually have. We can then recommend the best way to go ahead with as to, what to ask the electrician to quote against...

I would however recommend, that you do install an earth rod (2 X 5/8'' coupled together for depth) at each of the 2 outbuildings as a matter of course. Connecting these 2 additional rods with the house's main rod will not only serve the two outbuildings, but also lower the overall Ra value, which serves the main house installation too!!

Graet, thanks for that. I will upload photos ASAP. As forthe coupled rods, I should be able to do that without hitting any services, that is if the drawings are right.

 

[Deleted member 73437]

if you can manage to get a rod through the foul drains, the Ra should become good every time the bog gets flushed. :ciappa:

I'll let you know if the neighbours start complaining of a foul smell!

 

[GLENNSPARK]

I'll let you know if the neighbours start complaining of a foul smell!

just out of interest...where is that rod sited in relation to the building?

 

[Deleted member 73437]

just out of interest...where is that rod sited in relation to the building?

To put things into context, the building is a bungalow. The rod is not copper but looks like steel, how long it is I don’t know. It is situated about six inches from the wall.The earth cable goes through the wall up the cavity to the CU. The overall distance from the rod to the CU is 12 to 15 ft. I intend to have a further two rods fitted, of the type suggested by Engineer54, one outside each of the outbuildings.

 

[telectrix]

come at least 4ft. from the building/s. that will miss the rubble that the idle builder has buried, and use a decent earth pit.

 

[GLENNSPARK]

To put things into context, the building is a bungalow. The rod is not copper but looks like steel, how long it is I don’t know. It is situated about six inches from the wall.The earth cable goes through the wall up the cavity to the CU. The overall distance from the rod to the CU is 12 to 15 ft. I intend to have a further two rods fitted, of the type suggested by Engineer54, one outside each of the outbuildings.

what he`s on about is getting several 5/8" rods and connecting them together to form one long rod.....you dig a pit first as Tel says...this is to ensure you arn`t going to hit any buried services with any rods you drive into the ground....once you have dug the pit and are sure you wont intercept any pipes and/or service cables etc...then you drive the first rod in.....then you connect the second rod to the first and carry on drivin it in...this is what eng is saying about stable Ra values being obtained....
depth is key with TT.....

 

[Deleted member 73437]

Thanks, yes I can manage that. So basically the system is OK with 3 CUs but the following needs to be upgraded:

1. The 32mA MCB in the main CU to 40mA.
2. The earthing system

Will this work constitute ´new works´ and affect the whole circuit from the main CU to the workshop and as a consequence require the whole circuit to be replaced to present standards?

 

[telectrix]

not if the existing cable etc. are in safe condition and "fit for continued use".

 

[Engineer54]

Mittel, first post up the photo's on here, then we can advise as to what options your going to have, that can be quoted against with your electrician. The first thing you can ask him to provide, is the measured Ra value of your existing earth rod.


What sort of distances are we talking about, between the main house and the two outbuildings??

 

[Deleted member 73437]

Mittel, first post up the photo's on here, then we can advise as to what options your going to have, that can be quoted against with your electrician. The first thing you can ask him to provide, is the measured Ra value of your existing earth rod.


What sort of distances are we talking about, between the main house and the two outbuildings??

I appreciate that you are limited as to what advice you can give and that photos of the system will give you a better idea however, I’m not very good at uploading /downloading gizmos so I’ve asked my daughter to come over and do it for me.

As for the distances, the garage is about 4 meters from house and the garage to the workshop, CU toCU, is about 35 meters.

I have been informed that if I contact the distribution company they will do an earth test and if needed fit a "Protective MultipleEarth"

 

[Deleted member 73437]

not if the existing cable etc. are in safe condition and "fit for continued use".

ll there is power and light in the two outbuildings and the preious owner run it as a proper workshop with lathe and a number of other woodworking machinery,but that is not to say that it is "fit for continued use". So that´s another one on my list to discuss with the electrician. Many thanks.

 

[GLENNSPARK]

ll there is power and light in the two outbuildings and the preious owner run it as a proper workshop with lathe and a number of other woodworking machinery,but that is not to say that it is "fit for continued use". So that´s another one on my list to discuss with the electrician. Many thanks.

reason CSA has been asked here and length of run is for volt drop.....
thats why their askin....

 

[Engineer54]

I have been informed that if I contact the distribution company they will do an earth test and if needed fit a "Protective MultipleEarth"

That would be the better option as far as system earthing is concerned, but may also involve you having to run a new supply cable to either one or both of the outbuildings if they have any extraneous earthed services within them, such as a metallic water service pipe. In order to comply with PME requirements you'll need a 10mm bonding cable connection between the main house MET and the bonded pipework. Which can be via a single 10mm bonding cable, or a new 10mm 3 core SWA cable replacing the existing cable.

I remember you saying that the existing supply cable was a 10mm T&E in heavy wall conduit/pipe, if the pipe is large enough, then the single 10mm cable can be pulled into this existing pipe....

 

[GLENNSPARK]

That would be the better option as far as system earthing is concerned, but may also involve you having to run a new supply cable to either one or both of the outbuildings if they have any extraneous earthed services within them, such as a metallic water service pipe. In order to comply with PME requirements you'll need a 10mm bonding cable connection between the main house MET and the bonded pipework. Which can be via a single 10mm bonding cable, or a new 10mm 3 core SWA cable replacing the existing cable.

I remember you saying that the existing supply cable was a 10mm T&E in heavy wall conduit/pipe, if the pipe is large enough, then the single 10mm cable can be pulled into this existing pipe....

rods more cost effective here eng....and if he gets it right with them.....

 

[Deleted member 73437]

That would be the better option as far as system earthing is concerned, but may also involve you having to run a new supply cable to either one or both of the outbuildings if they have any extraneous earthed services within them, such as a metallic water service pipe. In order to comply with PME requirements you'll need a 10mm bonding cable connection between the main house MET and the bonded pipework. Which can be via a single 10mm bonding cable, or a new 10mm 3 core SWA cable replacing the existing cable.

I remember you saying that the existing supply cable was a 10mm T&E in heavy wall conduit/pipe, if the pipe is large enough, then the single 10mm cable can be pulled into this existing pipe....

There are no other services to either the garage or the workshop. The workshop is of timber construction with tiled roof and the garage is standard brick.

 

[Deleted member 73437]

rods more cost effective here eng....and if he gets it right with them.....

I understand what you´re saying but on the other hand I´ll get peace of mind that the earthing system is up todate and effective.

 

[GLENNSPARK]

I understand what you´re saying but on the other hand I´ll get peace of mind that the earthing system is up todate and effective.

well then apply for a PME connection then....yes, its a more reliable means of earthing....what eng was getting at was if there was any extranious in that garage/outbuilding then you would`v had to extend the equepotential zone with a length of 10mm CSA g/y...
dont forget as well that you may want to upgrade any main bonding in the house if you go for TN-C-S....
definately if less than 6mmCSA

 

[Engineer54]

rods more cost effective here eng....and if he gets it right with them.....

Nothing to stop him including the outbuilding earth rods into the PME earthing system. In fact it is preferable and will make any new PME system that much safer, if ever a neutral fault developed on the system, especially if he gets nice low Ra values on those rods!! lol!!

 

[GLENNSPARK]

Nothing to stop him including the outbuilding earth rods into the PME earthing system. In fact it is preferable and will make any new PME system that much safer, if ever a neutral fault developed on the system, especially if he gets nice low Ra values on those rods!! lol!!

yep...good backup eng...
in fact...i distinctly remember a few days ago...we had a TN-S with a rod....the O/P disconnected the rod therefore creating an extranious conductive part right next to the head....
from what i remember you advised him to reconnect...pronto...

 

[Engineer54]

yep...good backup eng...
in fact...i distinctly remember a few days ago...we had a TN-S with a rod....the O/P disconnected the rod therefore creating an extranious conductive part right next to the head....
from what i remember you advised him to reconnect...pronto...

Yes, ...I remember that too ...lol!!