Ring Final In 4Mm

[soulman]

Hi, came across a ring wired in 4mm, on a 40a mcb. They had lived in the property since it was built 20 years ago, so it has always been there. 3 bedroom house whole house on the ring. Has anyone came across this before. I have come across radial socket circuits on a 40a breaker and i fused them down to 32a.

Cheers

 

[Steve3948]

Worked on MOD jobs where the spec called for 4mm² Ring Main, but never seen it in a domestic, was the building used for business or growing weed.

 

[soulman]

Steve, this was a domestic property, i was working on the lighting circuit and noticed the board only had 40a breakers in & 6a for lights, one ring which i thought was 2.5 at first then realised it was 4mm. 40a for shower, 40a for cooker, most cookers i see are on 32a. The owners said that the electrics haven't been touched since they purchased house. I have asked a few sparks & they have never seen a 4mm ring ever and said i must be mistaken they will be 4mm radials on wrong breaker.

 

[NozSpark]

Are you 100% sure that it's 4.0mm and not 7/.029 or 7/.036???

 

[springcrocus]

If you've measured an end-to-end, then it's a ring.

Nothing wrong with 4mm rings on a 40A except that the cpc is still only 1.5 so might limit the length a bit. Also, spurring might be a tad difficult, trying to get three conductors in the terminal.

 

[springcrocus]

Are you 100% sure that it's 4.0mm and not 7/.029 or 7/.036???

If it was, Noz, the cpc would be a three-wire stranded. Metric is a single wire. The OP hasn't given us that info, though

 

[soulman]

All cpc's were solid, i didn't check if it was a ring or not, i advised the owners to have it checked out, thats when they told me it has never been touched.

 

[ProDave]

All cpc's were solid, i didn't check if it was a ring or not, i advised the owners to have it checked out, thats when they told me it has never been touched.

Why didn't you check it? it would have taken all of 5 minutes.

 

[soulman]

Hi Dave, you weren't there mate, i was giving a quote for some downlights, I was checking the lighting circuit out, when i said to the customer thats a bit unusual, after i had already had a bit grief from the customer for checking bonding under the sink, when she had to remove a few cleaning products. I also had to give the customer an explanation to why i needed to see the bonding was in place. As i was giving a quote, i didn't want the customer to think that i was on the make. So i simply said that circuit may need further investigation & explained. If i am back for the job then i would almost certainly take a look.

 

[Revved Up Sparky]

On an old installation you've also got the possibility that, over the years, spurs/ spurs off spurs have since been added, perhaps in 2.5mm. If heavy loads were then connected to the spur/s you could have 40A flowing through a section of cable that can safely carry much less current. If the OPD remains at 40A I would therefore recommend the circuit be thoroughly inspected in order to ensure this is not the case.

 

[ProDave]

Yes very difficult if you were only there to give a quote. I thought you were there actually working on the lighting circuit, so it would have been simple just to check, then you could advise.

but if it's a difficult customer, you probably don't even want the lighting job anyway.

 

[Barx]

Installed many 4mm rings in bungalows and upstairs flats whne ring is passing through plenty of insulation. Clerk of works called for it.

 

[PC Electrics]

If it's two 4mm radials wired into 1 40A mcb, then the cables are not adequately protected. Might be that someone was ahead of the times and wired it to account for insulation (a 40A ring requires the ccc of the conductors to be 25A). Although only one rfc in a property would generally not be considered best practice even 20 years ago.

To be fair, you did tell us at the top of the thread that this is a ring, then further down told us you didn't know if it is or not?? Before sentence can be pronounced we need to know the facts.

 

[andy_spark]

Reg 433.1.103: Accessories to BS 1363 may be supplied through a ring final circuit, with or without unfused spurs, protected by a 30 A or 32 A protective device...

Regardless of the cable size, or if it is a ring or not, it's incorrectly protected.

 

[Steve3948]

Reg 433.1.103: Accessories to BS 1363 may be supplied through a ring final circuit, with or without unfused spurs, protected by a 30 A or 32 A protective device...

Regardless of the cable size, or if it is a ring or not, it's incorrectly protected.

Except its fused at 40A !!! :innocent

 

[andy_spark]

Except its fused at 40A !!! :innocent

That's my point. The OP's 40A circuit needs to be downrated.

 

[Steve3948]

That's my point. The OP's 40A circuit needs to be downrated.

Hahaha, did your edit change correctly to incorrectly by any chance, or am I needing glasses.

 

[andy_spark]

I edited because I spelt protected wrong.

 

[Steve3948]

I edited because I spelt protected wrong.

My bad than sorry, I must be getting dyslexic in my old age, seeing something thinking other :red card

 

[andy_spark]

I often see something and think about (wish for) something else!