Help with specs!

this job is not guess work there is a lot going on in the background, I would not try and frame up a barn by reading a few books and watching u-tube videos

No, and you shouldn’t, which is why I hired an electrician and consulted many forums and calculators to arrive at the specifications I, and the electrician, did.

I trenched in the cable, mounted and wired the sockets and lighting, made off the SWA, installed the consumer unit and purchased other bits. All of that is done to regs, tested and working. I sent them regular photos, which they approved, and I left the rest for them, which I wasn’t totally confident with.

After seeing the electricians work, hearing their original specs and what they are now suggesting, I am looking for help. That is exactly why I am here asking these questions.. I’m asking people like you, an electrician of 50 years, for help and expertise. If seems like all you can offer is short, patronising and uninformative advice at this stage!

I know you are a self-titled old git but why not appreciate that I am not some social media zombie who doesn’t want to learn anything; I’m trying to expand my electrical knowledge and skills with help from professionals and forum communities, so why don’t you stop being a grumpy old bastard and help?

I haven’t just been down to B&Q and picked up any old cable and chosen which colour I like the best for any old terminal.

Shocker1 said:

As I am a DIYer, I felt it best to just use 3 core rather than trying to use the steel wire as my ground, I am more comfortable with the extra copper core. Even if I am at the top end of what I will be running, I don’t think I’m concerned about the 6mm being the issue?

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I'd be inclined to give voltage drop a bit more consideration. There's a good reason why BS7671 specifies maximum percentages and all of the equipment you have listed for that workshop will be affected at your expected average loading.

Shocker1 said:

I would really love some more detailed information if you have some to offer, rather than such vague short answers? I truly wish to learn more, but I’m not really getting much from you other than perhaps you think the cable should be 10mm 2 core and not 6mm 3 core?

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The member you responded to here has outlined in post #2 the minimum information required in order to possibly provide an answer to your question. Without those test results any answer would be nothing more than guess work.

Specifying cable size and protective devices can quite an involved process. It can be shortened considerably through the application of knowledge and experience, but Ze and PSC would be crucial in providing an answer to your question.

nicebutdim said:

I'd be inclined to give voltage drop a bit more consideration. There's a good reason why BS7671 specifies maximum percentages and all of the equipment you have listed for that workshop will be affected at your expected average loading.



The member you responded to here has outlined in post #2 the minimum information required in order to possibly provide an answer to your question. Without those test results any answer would be nothing more than guess work.

Specifying cable size and protective devices can quite an involved process. It can be shortened considerably through the application of knowledge and experience, but Ze and PSC would be crucial in providing an answer to your question.

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Excellent, thank you. I’ll get that information tomorrow.
Very worrying now to think the sparky spec’d 4mm originally… This is why I’m so concerned about the rest of his suggestions and work. Your input is invaluable, much appreciated!

Shocker1 said:

No, and you shouldn’t, which is why I hired an electrician and consulted many forums and calculators to arrive at the specifications I, and the electrician, did.

I trenched in the cable, mounted and wired the sockets and lighting, made off the SWA, installed the consumer unit and purchased other bits. All of that is done to regs, tested and working. I sent them regular photos, which they approved, and I left the rest for them, which I wasn’t totally confident with.

After seeing the electricians work, hearing their original specs and what they are now suggesting, I am looking for help. That is exactly why I am here asking these questions.. I’m asking people like you, an electrician of 50 years, for help and expertise. If seems like all you can offer is short, patronising and uninformative advice at this stage!

I know you are a self-titled old git but why not appreciate that I am not some social media zombie who doesn’t want to learn anything; I’m trying to expand my electrical knowledge and skills with help from professionals and forum communities, so why don’t you stop being a grumpy old bastard and help?

I haven’t just been down to B&Q and picked up any old cable and chosen which colour I like the best for any old terminal.

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Recorded result for Zs will be on the test cert. PFC will also be recorded there and should be sufficient for this application.

Probably best not throwing insults at people form whom you wish to solicit help.

nicebutdim said:

Recorded result for Zs will be on the test cert. PFC will also be recorded there and should be sufficient for this application.

Probably best not throwing insults at people form whom you wish to solicit help.

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Good advice!

I am interested in where the earth rod is, and how it was tested and why you think you need one, if you have exported the earth from the mains?

poni said:

I am interested in where the earth rod is, and how it was tested and why you think you need one, if you have exported the earth from the mains?

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Good question poni; this was the Sparky’s say. He turned up with it on the morning he came and said “fit this where the SWA enters the wall into the outbuilding..

I think I need one because the electrician said so, simple as that. As time has gone on and I’ve seen his work and sought third party advice about his recommendations, I’m asking these very questions. This is partly why I want to know more, so I am better equipped to understand the choices and recommendations of any tradesman. I’ve just moved to this area, so all the other tradies are new to me, not the ones I’ve been working with for years. This guy was recommended and I’ve tried to be patient as it is a village and I know things don’t work the same in yee old country, but that’s no excuse for bad advice and poor workmanship.. Let alone when it can have dangerous and deadly consequences! Forget about having to come down to the house if something trips, at this stage I’m worried about touching my planer and getting fried!

"I have a decent idea of what I'm doing", no you don't.
I don't need to do any calculations my experience tells me the 6.0mm² submain is undersized, I guarantee your lights will dip when you turn on one of your machines.
Volt drop must be considered for the entirety of the installation it does not stop at the end of the submain. This project was going wrong the moment you put the spade in the ground to dig the trench.
The two clowns you have employed are merely masquerading as electricians or they would have pointed out the errors of your ways.

Now that is helpful advice, thank you.

I know how to do groundworks, how to trench and lay cable, how to wire a circuit and make off SWA. What I don’t know, as I said, is how to design and spec a system in its entirety. This, I did not do; I asked the village to recommend an electrician and one turned up.

If you know how to use a saw, a chisel, and join timbers, you can say you know what you’re doing. You would not say you know how to design a frame comprehensively, considering structural loads and seasoning or timber movement. You would hire someone, and work within your parameters, as I said, and as I did.

Hopefully we can get past the patronising and just to more helpful info!

So, aside from making sure those idiots never return, my choices are what? I have 30mm conduit in the ground, it’s a pretty continuous run without sharp turns/bends, but I don’t know how I fancy my chances of trying to pull 10mm SWA through there over that distance! What about pulling through a smaller, additional SWA and running the lights off of a different circuit?

There is already a 4mm running into the garage, which successfully powers the sockets and lights even when running a saw and two extractors without any dipping in the lights. It runs about 30m. However, it isn’t really a legitimate or safe source of power and I don’t want to use that, which is why I’m running new SWA in. I could run the lighting circuit, or even the smaller socket circuit from the existing and run my machines off of the 6mm?

Nothing ideal here but just considering options..

are you just going to keep asking until you get the answer you want or are you going to listen and get a competent electrician to look at the job,
I am thinking that the earth rod is there because he was going to make the garage a TT supply, while we are on the subject of supply what are your supply characteristics, TT, TNCS or TNC?

do they make 30mm conduit ?,

do you know there is a difference between "buried" and "run in conduit" , when we are talking about cable runs

this is not a game, remember someone can die from your mistakes, just like using the wrong timber to make a barn, and because it works, does not make it safe

The SWA is buried.. other services are inside the conduit. So yes, I understand the difference. And yes I understand the risks. Which is why I’m here, asking for your help, rather than continuing to have this system wired up, so we can avoid anything bad from happening to anybody. I’m not sure what you’re not grasping about that..

I will absolutely not allow that system to go live until I am certain a competent electrician has inspected, worked on, and signed off. Again, that is why I am here seeking as much advice and knowledge as possible

Shocker1 said:

I will absolutely not allow that system to go live until I am certain a competent electrician has inspected, worked on, and signed off

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then leave him to do his job , as you will need a completion certificate to hand into the local council , and not just a EICR ,

Shocker1 said:

The SWA is buried.. other services are inside the conduit. So yes, I understand the difference. And yes I understand the risks. Which is why I’m here, asking for your help, rather than continuing to have this system wired up, so we can avoid anything bad from happening to anybody. I’m not sure what you’re not grasping about that..

I will absolutely not allow that system to go live until I am certain a competent electrician has inspected, worked on, and signed off. Again, that is why I am here seeking as much advice and knowledge as possible

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As previously stated; no one can answer your original question on the basis of information provided at this point.

A competent electrian wouldn't sign off any distribution circuit that exceeds maximum permissible voltage drop by such a degree, but you've basically dismissed that point. Arguing the toss about such concerns won't exactly encourage anyone to answer other questions, when a flagrant disregard is displayed about an issue you'd been unaware of. It's not simply a matter of lights flickering, which you probably won't notice with LEDs, but one of potential damage to motors and increased current draw which potentially has a knock on effect on suitability of cables and protective devices and there we have a problem with the very question to which you seek an answer.

Getting power from A to B is a relatively simple process. Doing so in a manner that meets regulatory requirements and, more importantly, will fail safely is slightly more involved.

Trying to pull another cable through the same conduit will be far harder than replacing with the 10mm - use the existing cable to pull it through.

Sounds like your local sparky is crap!

As for the members on here, this guy is listening, so enough of the criticism. Just deliver the bad news

Fair point • it was late and I didn't fully absorb that last post.

I see mention of other services in the same duct - it might be better to pull everything back with a rope tied on, than risk damaging them in such a small space.

As people have said there are too many variables to be able to give a full definitive answer. With the distance involved and the "potential" power usage I would have said a larger cable is far more appropriate. I spec 6mm as a minimum for a garage a few metres away from a property.

It sounds like the "electrician" has made the garage into a TT system which would explain the need for an earth rod. This more than likely means your incoming supply is a TNC-S or PME. Whilst its not wrong to export an earth from a PME system there are problems which can occur, and by making the workshop a TT system these are greatly reduced.

You mentioned there are other services run into the workshop. What is the bonding requirements for these ? Is it required ?

If you state your location a bit more locally than the UK then maybe someone on here might be willing to visit and cast an eye over the installation and give you some honest on the spot advice.

As others have said you should receive an Electrical Installation Certificate and the work needs notifying to building control in order to comply with Part P of the building regulations. You must ensure that the "electrician" supplies this, it would not comply if he provides you with an EICR (Electrical Installation Condition Report)

Whilst I appreciate that we all try and save ourselves some money by doing things that we feel we are capable of sometimes it does cause more problems than letting a qualified tradesman get on with the job as you will have a come back on them if things dont work. If he had installed a 4mm cable and you had problems with nuisance tripping then he would have been responsible for sorting out the problem. As it is you don't really have any come back if anything doesn't work out correctly.

Due to the too many cooks syndrome I fear that most electricians would want to rip it out and start again if they were expected to put their name to a legal document certifying the installation.

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What size protective is protecting this cable?

You need to exercise caution when using LEDs and rotating equipment.