16mm Sub-Main on 100A?

[JayeJaye]

Hey guys, so I'm new here and have a question.

A local venue I work for has recently has had some electrical work done in order to increase the amount of power available to them, by bringing a phase in from the shop next door.

Previous to this, the supply was 3ph, 100A, and they have had an additional 100A brought in on 16mm T+E cable (clipped), into a meter and then to the CU.

However, I had a phone call saying they can smell burning, and that the cable coming from the shop is hot to the touch. They sent a photo, and the earth sleeving has completely melted and gone black, and started encroaching on the insulation for the neutral, whilst the connector block for it is now bare, having melted its way through the plastic insulation.

I have no access to the shop next door, so I am not sure what the method of termination and connection is, or what the exact cable length is, however I was always under the impression that 16mm had a maximum current of ~85A when clipped direct?

Surely this should be in 25mm? Can someone please clarify?

Thanks

 

[snowhead]

There's a lot to be done before worrying about the size of cable being correct or not.

Whatever is connected to the 16mm t&E needs isolating immediately.
Access is needed to the shop and cable source to see if there is any damage to the cable or shop.

 

[JayeJaye]

There's a lot to be done before worrying about the size of cable being correct or not.

Whatever is connected to the 16mm t&E needs isolating immediately.
Access is needed to the shop and cable source to see if there is any damage to the cable or shop.

The landlord has called the sparks that fitted it, who haven't been on site, but have said it be doing what it's doing, and won't come on site. I have a feeling this is going to be a nightmare

 

[Darkwood]

The landlord has called the COWBOY that fitted it, who haven't been on site, but have said it be doing what it's doing, and won't come on site. I have a feeling this is going to be a nightmare

Corrected that for you.

As above, isolate all loads immediately! The cable is damaged and poses a risk to property and life, express this to the landlord that it needs disconnecting from the power asap, even if they have to force entry - a lock is cheaper to replace than the possible alternative.

 

[JayeJaye]

I was there at close of business last night, and we took all the load off the cable, isolated the CU it feeds, and that's all we could do. The damage is visible at the exit from the meter, but couldn't isolate that as the venue owner didn't want to break in, and landlord was away. We are all heading down there now, so will report back.

 

[Octopus]

I'm curious to know why you think the new sub main is 100a if you haven't seen the origin?

 

[Darkwood]

Something is def' wrong if the cable is getting red hot and melting, I actually suspect a lost N where a N/E fault has let the current return down the smaller earth wire overheating it hence the effects your seeing of it melting the earth sleeving and starting to melt into the N insulation, that or a network fault utilising the earth and overheating it.

I assume he has been informed the new supply was 100amp 1ph rather than seen it, as this is how I read the first post.

 

[JayeJaye]

Hey again.

Thanks for all of your replies, to answer some questions....

Last night when I attended site, we (the owner and I) moved all of the items on sockets to another supply, in order to preserve chilled food. Then isolated from the sub main board onwards.

Someone asked how I knew it was a 100A incomer from the shop..... I was informed, however wasn't aware what switch gear is down there.

The set up is as follows:

Shop main board > rotary isolator (100A) > 16mm T+E > meter > Consimer Unit > 63A breaker > kitchen DB

Hence why I was unable to isolate the whole run.

On to the hot earth wire and cable damage.

Sparkies turned up, said it wasn't their fault and re terminated the 16mm into the meter. All good, they left.

Kitchen opens and the cable starts to heat again. Current draw 62.9 amps.

Opened up first board after the meter....

Current on Earth - 62.9 amps

Neutral - 0

When they wired the SWA to the kitchen (moved off main DB from original supply), they wired the Earth and Neutral backwards.

Closed the kitchen, assessed any cable damage and corrected wiring. Cable cool, all working, all good.

Still not sure about 100A main switch on 15m run of 16mm but the 63A breaker is there for that circuit and there's nothing else on the board.

Thanks again

 

[Darkwood]

My last post was a very good call then ... I said lost N and earth been used for current return

 

[bigspark17]

Great call darkwood. Do you have pics of the incorrect wiring.? How on earth did they get it wrong???

 

[Simonslimline]

Great call darkwood. Do you have pics of the incorrect wiring.? How on earth did they get it wrong???

A sheer lack of competence i would of thought.

 

[JayeJaye]

The new incomer was twin and Earth, so brown and blue. That went into a board, as normal, as you would expect. The outgoing SWA is Brown Black Grey, and was wired Brown > L, Black > E, Grey > N.

The other end where it reached the kitchen DB was wired Brown > L, Black > N, Grey > E, putting the neutral load down the smaller earth conductor.

If only they had looked at the other board.... I missed it at first as a previous sparky had covered the coloured conductors of the SWA in tape to represent their function, however this wasn't a problem before, I can only guess they didn't look and just assumed.

 

[Simonslimline]

Was any testing carried out then?

Sounds like a right balls up.

 

[JayeJaye]

• Was any testing carried out then?

Sounds like a right balls up.

Kid you not, they literally shortened the cable and reconnected it to the meter, identical to how it was before, gave a thumbs up and left site. Didn't check the board or anything, just literally did that.

As soon as they had left I checked their repair, and on their instruction, the kitchen opened at full load. Within minutes the cable was heating up again, so I said to the owner, this isn't right. Give me a minute with it, clamp metered the conductors and saw the readings I mentioned, went to the other end and clamp metered again, readings for neutral and earth reversed. Picked tape off the conductor and found the balls up on the colours.

Sure, it could have been done quicker however landlord was adamant that his chaps come back to show it wasn't their fault, rather than sort it quicker.

 

[Simonslimline]

• 
  
  Kid you not, they literally shortened the cable and reconnected it to the meter, identical to how it was before, gave a thumbs up and left site. Didn't check the board or anything, just literally did that.
  
  As soon as they had left I checked their repair, and on their instruction, the kitchen opened at full load. Within minutes the cable was heating up again, so I said to the owner, this isn't right. Give me a minute with it, clamp metered the conductors and saw the readings I mentioned, went to the other end and clamp metered again, readings for neutral and earth reversed. Picked tape off the conductor and found the balls up on the colours.
  
  Sure, it could have been done quicker however landlord was adamant that his chaps come back to show it wasn't their fault, rather than sort it quicker.

• 
  
  So they were clearly not real electricians then. It really is a sad state of affairs to be honest that this kind of dangerous practice is delivered to paying customers.

 

[JayeJaye]

So they were clearly not real electricians then. It really is a sad state of affairs to be honest that this kind of dangerous practice is delivered to paying customers.

I did ask them about the situation where the earth would get so hot that it would char the sleeving and melt the connector block into a blob of goo on the floor. They said, and I'll quote:

"Love, you've got something in your kitchen that's got an earth fault, and that's what's doing it, let us fix this" and shoo'd me away!

So off I went scratching my head, thinking, hang on, one appliance which is getting an earth on a 16mm, so 10mm, that hot? It's all 13A sockets in there. That's a fair few faults.....!!!?

Maybe they don't like gingers

 

[Darkwood]

I would in your shoes send a detailed report expressing how dangerous the installation was and how basic testing that is required with any install would have picked it up, I would also ask him for copies of the certificates of there work..... i bet they never handed any over, brownie points for you and possible future work.

 

[Simonslimline]

I did ask them about the situation where the earth would get so hot that it would char the sleeving and melt the connector block into a blob of goo on the floor. They said, and I'll quote:

"Love, you've got something in your kitchen that's got an earth fault, and that's what's doing it, let us fix this" and shoo'd me away!

So off I went scratching my head, thinking, hang on, one appliance which is getting an earth on a 16mm, so 10mm, that hot? It's all 13A sockets in there. That's a fair few faults.....!!!?

Maybe they don't like gingers

A 16mm2 Flat twin and earth only has a 6mm2 CPC by the way.

1.0 sqmm cable has 1.0 sqmm CPC
1.5 sqmm cable has 1.0 sqmm CPC
2.5 sqmm cable has 1.5 sqmm CPC
4 sqmm cable has 1.5 sqmm CPC
6 sqmm cable has 2.5 sqmm CPC
10 sqmm cable has 4 sqmm CPC
16 sqmm cable has 6 sqmm CPC

 

[JayeJaye]

A 16mm2 Flat twin and earth only has a 6mm2 CPC by the way.

1.0 sqmm cable has 1.0 sqmm CPC
1.5 sqmm cable has 1.0 sqmm CPC
2.5 sqmm cable has 1.5 sqmm CPC
4 sqmm cable has 1.5 sqmm CPC
6 sqmm cable has 2.5 sqmm CPC
10 sqmm cable has 4 sqmm CPC
16 sqmm cable has 6 sqmm CPC

My mistake, sorry it's been a v long night with weather damage on top of this mess!!

 

[Simonslimline]

My mistake, sorry it's been a v long night with weather damage on top of this mess!!

On that note i don't know why i am still up either.

Signing out. Take it steady