What would you code this as.

Electrics · Oct 31, 2021

Taylortwocities said:
The 40A is thd maximum current that the RCD contacts have been tested to handle reliably. If you put 50smps through it then the contacts could burn out or (worse) weld together. Then the supply will not cut should an earth fault trips the RCD.
The circuit needs current limiting at the source to protect the cable itself and anything else downstream.

Thanks for the explanation, i suspected as much but wanted to ask to be sure.

7029 dave · Oct 31, 2021

Electrics said:
I'm also very confused by the thread.

Why would you C2 a circuit for having the potential to pull higher amperage? Wouldn't we then just condemn every installation with 100a cutout since the lights and sockets the tails feed are wired in 1.5 and 2.5mm and so could 'potentially pull 100a'?

Lost.

But they are fused/ mcb rated

Pretty Mouth · Oct 31, 2021

It's an interesting question, and here are my thoughts. I'm interested to hear what other forum members make of them.

The downstream breakers at the outbuilding CU total 22A, so I do not believe overload of the 6mm cable is possible as it is. I think 433.3.1 would apply here, which would allow omission of overload protection if fault current protection is provided upstream.

So does the cable have fault protection? The regs say no, we're not supposed to rely on the DNO's device, so it needs coding.

However, the DNO's device is there, upstream of the 6mm cable, we can all see it. I would say if the cable met adiabatic requirements for the DNO's 100A fuse , then I would give it a C3. If it didn't meet adiabatic requirements, then C2.

@Raptor0014 , read 433 through to 436 in BS7671, and see what you make of it. I've attached fault curve for BS1361 fuses. As other members have pointed out, there seem to be gaps in your knowledge which really should be filled before you carry on with EICRs.

Electrics · Oct 31, 2021

7029 dave said:
But they are fused/ mcb rated

I know that's why it doesn't make sense to me. Why be worried about the fact that the main incomer is 80a when the swa will never pull that because it's feeding lights and sockets? Basically no matter the rating on the main incomer that cable load side can never pull enough to be dangerous since the shed end has MCB protection no?

Basically won't the light/sockets 6a/16a MCB's simply trip before that 6mm SWA possibly has a chance to overheat?

The 6mm SWA goes downstream to RCD/MCB protection. Why is this different from main 100a breaker in a board feeding a 40a RCD? Shouldn't we also, according to OP, be concerned about the wires from breaker to RCD in that case? Is that what he's saying?

Like as we stand on a normal installation we have:

100a main fuse ----> 100a main breaker ----> 63a RCD

Here we have:

100a main fuse ----> 40a RCD

I don't see the difference....is there one?

7029 dave · Oct 31, 2021

The 6mm cable is basically a sub main feeding the 2way CU in the out building, therefor a suitably sized s/fuse should be fitted at the supply end to protect the cable , at present its relying on the DNO fuse.
To add not terminated correctly/ no glands/ single insulation exposed / poor install to say the least.

Vortigern · Oct 31, 2021

The point of the fuse preceding the cable is that the fault current in the cables cannot reach a point that the cables would basically melt/explode due to current. i.e. the fuse is there to protect the cable so we would expect to find the rating of the fuse before the cable supplying the next submain would be lower then the cable rating in very simple terms. There is no way of knowing that in the future someone would not increase that load. But I am thinking of a short on the cables coming from the henley box that would be the problem there.

Electrics · Oct 31, 2021

7029 dave said:
The 6mm cable is basically a sub main feeding the 2way CU in the out building, therefor a suitably sized s/fuse should be fitted at the supply end to protect the cable , at present its relying on the DNO fuse.

What's the difference electrically between this coming from 100a incoming fuse to RCD protection in the shed and a regular 100a supply going to RCD protection in a CU?

Raptor0014 · Oct 31, 2021

There are some people in this forum that are jumping on the wrong bandwagon here. Maybe you should all take a deep breath and actually read the OP properly and if unsure ask me questions.

Rather than reply to every post individually I will update here.

Firstly yes I am a fully qualified, and registered with CPS, electrician. However, although qualified I lack experience as have only been fully qualified etc since Feb.

I am fully aware there are a no. of issues and I have coded them already on the certificate.

Eg,

SWA not terminated (it is glanded at the other end)
Single insulation exposed
Cables not supported
Undersized cable in relation to the OCPD (the cutout which is the query I had)
The covers for the connectors are actually just balancing (which you can't tell from the pic)
There is no earth sleeving/tape on the black insulated conductor

When I do the certificates I like to ensure I give the client as much accurate information as possible.

I was asking specifically about the size of the SWA and the fact there is no OCPD. I even stated in the OP that I had coded it as a C2. Maybe I should have been clearer but what I was getting at was my C2 code correct or did anyone think it warranted a C1?

The client mentioned it has been fine for the last 8yrs or so and I said they had been lucky then as there is nothing to stop that cable pulling 80a when it's designed at most to pull 47a if it were clipped direct.

I am acutely aware that my qualifications don't trump experience. I knew it was wrong, I had already coded it as such. What I wanted to ensure was that I was giving the client accurate information.

The one thing I will ALWAYS do if I am unsure is ask, hence my post here, even if it opens me up for potential ridicule. I'd rather be thought a fool and learn by asking a question, than keep quiet and get it wrong.

Peace, out!!

freddo · Oct 31, 2021

Raptor0014 said:
Maybe I should have been clearer but what I was getting at was my C2 code correct or did anyone think it warranted a C1?

I'd go for C2.

Pretty Mouth · Nov 1, 2021

Raptor0014 said:
There are some people in this forum that are jumping on the wrong bandwagon here. Maybe you should all take a deep breath and actually read the OP properly and if unsure ask me questions.

Rather than reply to every post individually I will update here.

Firstly yes I am a fully qualified, and registered with CPS, electrician. However, although qualified I lack experience as have only been fully qualified etc since Feb.

I am fully aware there are a no. of issues and I have coded them already on the certificate.

Eg,

SWA not terminated (it is glanded at the other end)
Single insulation exposed
Cables not supported
Undersized cable in relation to the OCPD (the cutout which is the query I had)
The covers for the connectors are actually just balancing (which you can't tell from the pic)
There is no earth sleeving/tape on the black insulated conductor

When I do the certificates I like to ensure I give the client as much accurate information as possible.

I was asking specifically about the size of the SWA and the fact there is no OCPD. I even stated in the OP that I had coded it as a C2. Maybe I should have been clearer but what I was getting at was my C2 code correct or did anyone think it warranted a C1?

The client mentioned it has been fine for the last 8yrs or so and I said they had been lucky then as there is nothing to stop that cable pulling 80a when it's designed at most to pull 47a if it were clipped direct.

I am acutely aware that my qualifications don't trump experience. I knew it was wrong, I had already coded it as such. What I wanted to ensure was that I was giving the client accurate information.

The one thing I will ALWAYS do if I am unsure is ask, hence my post here, even if it opens me up for potential ridicule. I'd rather be thought a fool and learn by asking a question, than keep quiet and get it wrong.

Peace, out!!

Fair play @Raptor0014 , hope you won't be deterred from asking in the future ?

MJPD29 · Nov 1, 2021

Raptor0014 said:
Doing an inspection and came across this.

Feeds are as follows:

Cutout to Meter - 25mm
Meter to connector blocks - 25mm
Connector blocks to CU’s (2 in the house) 16mm.

So far so good as the cutout is 80A not the 100A it’s labelled as.

My query is the 6mm 3 core XPLE that’s going to an outbuilding.

At the outbuilding end is 2 way CU with a 40 RCD switch and a 16a socket & 6a light circuit.

Now I know the RCD will stop the cable ever pulling more than 40A. But as it’s wired into those connectors it has the potential to pull 80a (in theory).

I’ve coded it as a C2 as to me it’s potentially dangerous given there’s no OCPD protecting the cable from the connector until it reaches the RCD in CU in the outbuilding. It’s been there approx 8yrs according to the owner and there are no signs of thermal issues anywhere at either end. But thought I’d garner opinion from the more experienced/knowledgeable folk on here.

What would you code it as? Or would you deem it safe given the RCD at the other end?

View attachment 91498

The RCD will most definelty not stop the cable from pulling more than 40a. It offers no overload protection whatsoever. As for your coding your correct with c2.

ferg · Nov 1, 2021

Raptor0014 said:
There are some people in this forum that are jumping on the wrong bandwagon here. Maybe you should all take a deep breath and actually read the OP properly and if unsure ask me questions.

Rather than reply to every post individually I will update here.

Firstly yes I am a fully qualified, and registered with CPS, electrician. However, although qualified I lack experience as have only been fully qualified etc since Feb.

I am fully aware there are a no. of issues and I have coded them already on the certificate.

Eg,

SWA not terminated (it is glanded at the other end)
Single insulation exposed
Cables not supported
Undersized cable in relation to the OCPD (the cutout which is the query I had)
The covers for the connectors are actually just balancing (which you can't tell from the pic)
There is no earth sleeving/tape on the black insulated conductor

When I do the certificates I like to ensure I give the client as much accurate information as possible.

I was asking specifically about the size of the SWA and the fact there is no OCPD. I even stated in the OP that I had coded it as a C2. Maybe I should have been clearer but what I was getting at was my C2 code correct or did anyone think it warranted a C1?

The client mentioned it has been fine for the last 8yrs or so and I said they had been lucky then as there is nothing to stop that cable pulling 80a when it's designed at most to pull 47a if it were clipped direct.

I am acutely aware that my qualifications don't trump experience. I knew it was wrong, I had already coded it as such. What I wanted to ensure was that I was giving the client accurate information.

The one thing I will ALWAYS do if I am unsure is ask, hence my post here, even if it opens me up for potential ridicule. I'd rather be thought a fool and learn by asking a question, than keep quiet and get it wrong.

Peace, out!!

This is unfortunately the nature of internet forums sometimes.

In fairness this one is not too bad in comparison to others. The mods here made a real effort to get it that way and continue to make an effort to keep it so.

Electrics · Nov 1, 2021

Raptor0014 said:
The client mentioned it has been fine for the last 8yrs or so and I said they had been lucky then as there is nothing to stop that cable pulling 80a when it's designed at most to pull 47a if it were clipped direct.

How were they lucky? Sorry i'm confused.

Cables don't just pull 80a just because they're attached to an 80a fuse.

If he's only got lights and sockets on the end of that SWA which are also RCD/MCB protected i fail to see how it can ever pull 80a. Even if you put five hundred electric rads in the shed the shed's CU will trip long before that cable can ever pull more than 80a, surely?

Or am i getting this totally wrong?

Julie. · Nov 1, 2021

Electrics said:
How were they lucky? Sorry i'm confused.

Cables don't just pull 80a just because they're attached to an 80a fuse.

If he's only got lights and sockets on the end of that SWA which are also RCD/MCB protected i fail to see how it can ever pull 80a. Even if you put five hundred electric rads in the shed the shed's CU will trip long before that cable can ever pull more than 80a, surely?

Or am i getting this totally wrong?

Because it's not just overload that an overcurrent device protects against, if there were to be a fault at the remote end of the swa then it could draw say 150A, which would take 1000 or so seconds to blow the dno fuse (~100 secs at 200A etc) this could result in the swa overheating and causing fires.

Of course it depends on the Zs at the remote end, it could have a decent fault current level and blow the dno fuse earlier. But by having the correct size fuse for the overload protection and fault protection would eliminate this.

Arguably it doesn't need overload protection, but it must have fault protection, and the dno fuse is unlikely to achieve this, there is also a dno requirement to provide one's own fuse for longer runs

Electrics · Nov 1, 2021

Julie. said:
Because it's not just overload that an overcurrent device protects against, if there were to be a fault at the remote end of the swa then it could draw say 150A, which would take 1000 or so seconds to blow the dno fuse (~100 secs at 200A etc) this could result in the swa overheating and causing fires.

Of course it depends on the Zs at the remote end, it could have a decent fault current level and blow the dno fuse earlier. But by having the correct size fuse for the overload protection and fault protection would eliminate this.

Arguably it doesn't need overload protection, but it must have fault protection, and the dno fuse is unlikely to achieve this, there is also a dno requirement to provide one's own fuse for longer runs

So electrically how is this different from the tails going from 100a incomer to CU?

What would you code this as.

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