What would you code this as.

Julie. · Nov 1, 2021

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

Compare the realistic Zs between an installation having a decent length of 6mm^2 and 1/2 metre of 25mm^2.

Also the 16 or 25mm^2 can take much more current than 6mm^2 before overheating the same.

HappyHippyDad · 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!!

Hi Raptor,

I haven't read the thread at all really as I have been up all night with raging tooth pain and at present have a bag of peas on my face.... lovely. Moving on to the point, I expect someone has mentioned it, but I think its important to emphasise it again as its a pretty major mistake and you have not mentioned it in your above post.

The RCD is 'rated' at 40A, meaning it can safely take up to 40A without getting damaged. It doesn't trip at 40A. If you have fitted an RCD before, thinking that the rating on it was overcurrent protection then you would need to go back and check it has another form of overcurrent protection if it needs it.

Keep asking ?

Raptor0014 · Nov 1, 2021

HappyHippyDad said:
Hi Raptor,

I haven't read the thread at all really as I have been up all night with raging tooth pain and at present have a bag of peas on my face.... lovely. Moving on to the point, I expect someone has mentioned it, but I think its important to emphasise it again as its a pretty major mistake and you have not mentioned it in your above post.

The RCD is 'rated' at 40A, meaning it can safely take up to 40A without getting damaged. It doesn't trip at 40A. If you have fitted an RCD before, thinking that the rating on it was overcurrent protection then you would need to go back and check it has another form of overcurrent protection if it needs it.

Keep asking ?

Hi Happy,

It’s not been fitted by me. I also made a mistake in my original post as it’s a RCCB in the outbuilding.

But thanks for the considered response.

Hope the tooth is better.

Electrics · Nov 1, 2021

Julie. said:
Compare the realistic Zs between an installation having a decent length of 6mm^2 and 1/2 metre of 25mm^2.

Also the 16 or 25mm^2 can take much more current than 6mm^2 before overheating the same.

But isn't it that the SWA isn't ever going to pull any more than the RCD/MCBs in the shed will allow?

I'm just confused as to how someone running a couple of lights and sockets off 6mm SWA has been 'lucky'?

Julie. · Nov 1, 2021

Electrics said:
But isn't it that the SWA isn't ever going to pull any more than the RCD/MCBs in the shed will allow?

I'm just confused as to how someone running a couple of lights and sockets off 6mm SWA has been 'lucky'?

That's overload.

Put a nail through the cable at the far end is fault current.

All (ish) parts of an installation must have fault current protection, which must disconnect in a suitable time without causing cable damage etc.

I doubt that a 100A fuse will provide that for a 6mm^2 cable of a reasonable length

telectrix · Nov 1, 2021

that 6mm SWA can withstand enough overload current for long enoughto fry the 40A RCD without even getting hot.

Electrics · Nov 1, 2021

Julie. said:
That's overload.

Put a nail through the cable at the far end is fault current.

All (ish) parts of an installation must have fault current protection, which must disconnect in a suitable time without causing cable damage etc.

I doubt that a 100A fuse will provide that for a 6mm^2 cable of a reasonable length

But how are you gonna damage it in normal circumstances, it's SWA.

Still a bit confused to be honest.

Is this one of those situations where it's against regs but in reality not all that dangerous?

Electrics · Nov 1, 2021

telectrix said:
that 6mm SWA can withstand enough overload current for long enough to fry the 40A RCD without even getting hot.

But what i don't get is the circuits attached to the MCB's attached to the RCD won't allow it so the device pulling the amperage will become disconnected before overheating of the SWA is possible?

So SWA->RCD->MCB->DEVICE, before the SWA can overheat 'because it can potentially pull 80a' as in the OP, the MCB will disconnect, stopping whatever it is that's pulling the amps, before the SWA even gets close to overshooting its rating, no?

Julie. · Nov 1, 2021

Electrics said:
Is this one of those situations where it's against regs but in reality not all that dangerous?

No, it is a real issue!

What do you mean

Electrics said:
But how are you gonna damage it in normal circumstances, it's SWA.

No fault is normal circumstances!

It isn't normal to drive a nail into a cable - but you will find loads of instances of "I was putting up a shelf and... or I was just putting this picture up and..."

Cable damage occurs -a lot!

[ElectriciansForums.net] What would you code this as.

Are examples of swa damage.

Faults happen, you need to protect against damage to the installation in the event it happens.

Electrics · Nov 1, 2021

Julie. said:
No, it is a real issue!

What do you mean

No fault is normal circumstances!

It isn't normal to drive a nail into a cable - but you will find loads of instances of "I was putting up a shelf and... or I was just putting this picture up and..."

Cable damage occurs -a lot!
View attachment 91536
View attachment 91537

Are examples of swa damage.

Faults happen, you need to protect against damage to the installation in the event it happens.

Im not saying these faults don't happen i'm asking about OP claiming the client was 'lucky' because the cable 'could pull 80a' because there's an 80a main fuse. I'm just talking about the installation as it is now not under a situation where it may develop a fault.

Isn't it only the equipment the other end that can pull 80a, which would never happen since it's lighting and sockets protected by 6 and 16 amp MCB's?

DefyG · Nov 1, 2021

If the SWA gets damaged, ie L-E or L-N fault, I should imagine the current will be a lot more than 80A, possibly nearer 800A (irrespective of whatever mcb’s/circuits are connected downstream), resulting in a fried cable and an expensive replacement for the sake of proper over current protection.

Vortigern · Nov 1, 2021

We are talking short circuit @Electric i.e. 1Kv. You know, fault of neglible impedance, PSCC-PEFC????

Julie. · Nov 1, 2021

Electrics said:
Im not saying these faults don't happen i'm asking about OP claiming the client was 'lucky' because the cable 'could pull 80a' because there's an 80a main fuse. I'm just talking about the installation as it is now not under a situation where it may develop a fault.

Isn't it only the equipment the other end that can pull 80a, which would never happen since it's lighting and sockets protected by 6 and 16 amp MCB's?

There is always the possibility of one of the downstream devices failing to trip - contacts weld together or the mechanism itself fails, upstream protection will limit the extent of an overload in these circumstances; nevertheless I would tend to agree, overload protection is probably not necessary on the swa, however fault protection still is, and as it's the same device its omission raises a c2.

The semantics aside the customer was lucky - especially given the numerous glaring issues that exist in merely this one photo.

littlespark · Nov 1, 2021

So you can do away with the 6A mcb for the lights as well as it will only be a fixed load of maybe 10W if LED? ?

It’s basic principles here…. MCB to protect the cable from fault as well as overload.

Electrics · Nov 1, 2021

littlespark said:
So you can do away with the 6A mcb for the lights as well as it will only be a fixed load of maybe 10W if LED? ?

It’s basic principles here…. MCB to protect the cable from fault as well as overload.

I thought MCB's only protected overload and RCD's protected earth faults?

What would you code this as.

Julie.

HappyHippyDad

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Raptor0014

Electrics

Julie.

telectrix

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Electrics

Electrics

Julie.

Electrics

DefyG

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Vortigern

Julie.

littlespark

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Electrics

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