Advice needed! Ive been to see a job for garage power, the previous electrician has taken a 4mm on a 32amp B MCB protected by a 30mA RCD. But hasnt done anything with, apart from the fact there is no protection and its T&E all straight forward. My ownly question is do i gland straight into a socket and then have a fuse spur to supply a light OR can i install a 2 way board protected by a main switch or does it need to be a RCD main switch.
- Thread starter Sparkzilla
- Start date
Why didn't the original Sparky finish the job???
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Dustydazzler
Your guess is as good as mine, customer said that he had said he was too busy.. i say the term electrician loosey, kitchen fitter with part p
How has the 4mm cable been installed.
Take through the ceiling of the ground floor, drilled out and slung in free air to the garage, my plan is to take it back to the house come down in 25mm conduit, dig a trench terminate aromoured, to either a 2 way board or socket.
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davesparks
What do you meant by no protection?
What protection do you think a main switch will provide?
Do you understand what an RCD is, how it works, and how it will work if you install another one in series with the existing one?
As soon as you contain it you can no longer use a 32A protective device. I would pull back into the house then use swa from this point.
i would where it comes through the brickwork on house straight into ipbox sealed to allow swa via a cantenary wire with metal zips into either a small consumer unit dont forget to check whether you need to slam a rod in as tt for external outbuildings, you wont need rcd board in here if its already protected at source due to which trips first,
As in twin swinging in the air.
I do indeed understand adding an RCD in series work. I was just asking if youd fit an rcd again in the garage
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Thanks mate, customer wants in buried, but everything else is spot on thanks mate
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Thanks mate
You either need the rcd at source or in the garage provided additional rcd protection is not required prior to the garage, you don't need both.
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davesparks
If you understand it then why ask the question as you must already know why it is pointless and likely to cause trouble down the line?
due to not being allowed by dno to transport pme to other buildings and or high earth readings,
Which DNO is that? I’d thought an earth rod would give higher earth readings than a pme supply.
western power is my area and ive been shoulder tapped by my governing body before on a visit
tt allows for higher than 35ohms at db
I’m not sure any DNO have any reservations on exporting/extending pme supplies in a domestic installation.
What Scheme are you with?
You are not exporting PME at all, what you are doing is extending a circuit to another building which happens to be derived from a PME source.
niceic
IF the outbuilding has NO exposed conductive parts & thus no introduced low resistance earth path then the PME can be exported.
e.g. total wooden shed on support battens with no pipework entering the shed...
This will meet BOTH of the above regs so OK exported.
Obviously if the house supply was TT or TNS the max fault current down the earth conductor would NEVER be the full load current. e.g. a broken neutral in these situations would just mean NO power!https://talk.electriciansforums.co.uk/uploads/emoticons/default_plain.gif
so only a smaller CSA earth needed to safely export earth.
which is why i said check not a must do.
You don't want to be listening to the non-collective opinions of the NICEIC. The presence of extraneous conductive parts is irrelevant providing the cpc of the supply cable to the building is adequate to support main protective bonding.
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Hi drilltoaster, I've had a good look into the whole 'DNO forbids exporting PME earth' thing, and it would appear to be a myth. I can find no evidence that any DNO outright forbids it, and neither can anyone else when challenged.
For western power, the best information I can find comes from their website, click on 'Can you provide an earthing terminal'
Western Power Distribution - Information for electrical installers
Western Power Distribution is the electricity distribution network operator for the Midlands, South Wales and the South West. You can contact us 24 hours a day, 7 days a week, 365 day a year.
In short, if everything meets BS7671 and Engineering Recommendation G12 then you're good to go.
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davesparks
I think it strictly means selling PME to another country, which is utter nonsense.
It is a phrase used incorrectly, usually by people who get their knowledge from rumours and what their mates tell them in the pub, to refer to extending the equipotential zone of a PME installation to outbuildings.
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A governing body tapped you on the shoulder???
Do you mean the assessor from a competent person scheme talked to you about this and you believed everything they told you without checking the facts and theory for yourself?
Hi drilltoaster, I've had a good look into the whole 'DNO forbids exporting PME earth' thing, and it would appear to be a myth. I can find no evidence that any DNO outright forbids it, and neither can anyone else when challenged.
For western power, the best information I can find comes from their website, click on 'Can you provide an earthing terminal'
Western Power Distribution - Information for electrical installers
Western Power Distribution is the electricity distribution network operator for the Midlands, South Wales and the South West. You can contact us 24 hours a day, 7 days a week, 365 day a year.www.westernpower.co.uk
In short, if everything meets BS7671 and Engineering Recommendation G12 then you're good to go.
i never said forbid
i got a dilemma for you
2 core swa installed in ground by house builder (major builder) already supplying a db in garage ze is 175 ohms what do you do?
scenario
customer wants a new consumer unit installed in the detached garage.
main incomer to building is on other side of house approximately 20 mtrs away new cable route if required is via grass and concrete, clay and rock is located in ground approximately 18inches if lucky.
i forgot to mention current ze is armour cpc
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davesparks
What on earth is that supposed to mean?
Ze is the EFLI of the DNO's service, it does not include any part of the installation.
it was a long time ago and yes while being assessed working for someone else and i had the unlucky visit with the company manager aswell so never really looked into it.
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20a mcb at board db1 measured at db2 rewirable fuse metal clad board
I assume you mean Zs not Ze as it is in the garage. If you have a Zs of 175 ohm then the circuit to the garage needs addressing as to why it is so high.
pme and ze at db1 if my memory serves about 22 omhs
bottom end i couldn't rely on the swa cable earth so installed a rod and isolated the gland earth connection at garage to stop parallel paths
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davesparks
Contact the DNO and get them to fix the high Ze.
No matter what you do with the garage supply the Ze will still be 175
i think we have covered to issue i miss abbreviated Ze as Zs
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davesparks
If the armour is not in good condition then the cable is damaged and must not be used. Installing an earth rod will not fix a damaged SWA cable.
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If the Ze is 22 ohms you still need to contact the DNO as it is way above what is acceptable.
That Ze needs addressing, and unless the swa is miles long, surely there is some reason why your zs is so massively high that you could look, into? Loose terminations or something? I'm not sure the solution to an unexpected Zs is to stick an earth rod in.
This is a slightly different scenario to the Op.
This is a slightly different scenario to the Op.
sorry 0.22 my bad (trying to quote and not preproofing what i reply)
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i wasnt looking to get roasted here i just put something out there and asked them to check
Ah, that seems more reasonable, that high zs would still need some investigating I think, using the armour as cpc would not account for that reading, and this situation doesn't mean that every outbuilding install needs an earth rod.
Not meaning to "roast" you buddy, I certainly don't know it all, just having a discussion... ?
Not meaning to "roast" you buddy, I certainly don't know it all, just having a discussion... ?
No one is trying to roast you. If you have a Ze of 0.22 and a Zs of 175 in the garage this points to a breakdown of earth continuity, the armour is almost certainly not effectively earthed.
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