solar cowboys report or not

[GaryM]

As I understand it, the 6mm2 cable isn't protected by a 63A OPD as I understand, it's connected with other incoming tails from the meter at the terminals of a main switch in another consumer unit.
From there it supplies a 2 way CU with a 63A RCD main switch. The consumer unit has two circuits, one 16A and one 6A. Considering that overload protection can be at the end of a circuit I reckon the 16A and 6A MCB's will provide suitable overload protection for the 6mm2 cable as the maximum demand of the consumer unit and cable will be 22A. As long as the cable is protected against fault current then it's safe enough.

I used an example above of a 400A busbar feeding multiple 63A switch fuse isolators. I can guarentee that the supplies to the isolators won't be rated at 400A.

There's more than one way to skin a cat.....it just doesn't mean that all ways are wrong, just different options of getting the same result.

 

[moggy1968]

It should have gone into a henley block, then be divided up. personally I would have used 16mm tails from there to the second DB, but thats a personal preference. As above 6mm probably ok given the total demand and protective devices in use (as per 431.1.1). Not a tidy bit of work and certainly not best practice but other than the cables not being securely fixed in the terminal I think you might be hard pressed to push for a breach of a specific reg. Always happy to be proved wrong though!!

 

[GaryM]

Thanks Moggy, exactly how I see it. For what it's worth, I too wouldn't have used 6mm2 and most definitely would have used a henley block but I look at things as if I were to carry out an EICR and if I can't state a specific regulation for a potential issue then you can't fault it, no matter how much you don't like it.

 

[BruceB]

As has been said from the overload protection perspective then 6mm will be fine.

From the fault current perspective you need to do the calculations as it is being protected by the service fuse. But it is also likely to be fine.

So it comes down to is the mechanical connection ok.

Remember the OSG is in some respects a short cut guide for those who do not want to do the calculations. The OSG will give a conservative, safe, but sometimes not the most economical answer.

 

[moggy1968]

with regard to fault current the way my assessor put it was this
In the event of a catastrophic short which will melt first, 16mm of tails or a skinny bit of fuse wire?

 

[BruceB]

Which is a fair way of looking at it sometimes, but inside a building you would want to make sure the 'skinny bit of fuse wire' will blow quickly enough that the thicker cable has not got hot enough to cause damage to things.

 

[moggy1968]

tails are usually visible though

 

[GaryM]

tails are usually visible though

You don't want to be replacing them though if the protective device didn't disconnect fast enough under fault conditions rendering the tails thermally damaged.

 

[spsparks]

The cable is fused by a 100A 1361 service fuse for gods sake. Read through section 712.............. The 6mm should have a 40A fuse in the DB at least or 25mm2 tails from "Henleys". The logic that suggests the service fuse protects the cable in the street would mean that at the end of each circuit should be a fuse. The 100A fuse protects the incomer from overloads and the ntails too. Any cable needs protected by a suitable fuse and 100A is not suitable for a 6mm cable. I find it difficult to believe some are defending this poor practice. Its fundamental stuff. How can a 100A fuse disconnect in enough time to stop a 6mm from bursting in to flames and setting the DB and tails alight too. I didnt come on here for a fight and had hoped for a better quality view. Its a shoddy job no matter what way you look at it and my client should not have been left in this situation. Neither should I have been put in the position of having to inform said client that the expensive job they have paid for is of doubtful technical quality.

 

[GaryM]

Overload protection can be at the end of a circuit but then again I feel like I'm flogging a dead horse here. If you came across this situation and falsely noted it as a defect on an EICR then I hope you have Professional Indemnity insurance!

Theres a two protective devices, 16 and 6A that will disconnect any overload, not the 100A main fuse.

I believe the situation has been made pretty clear by many posters so it's pointless continuing. If you think it's a problem then fine

 

[SolarCity]

I'm in agreement with GaryM on this. To be totally fair, it is a bit shoddy in my opinion but is there honestly anything wrong with it?

 

[BruceB]

...... Any cable needs protected by a suitable fuse and 100A is not suitable for a 6mm cable. I find it difficult to believe some are defending this poor practice. Its fundamental stuff.

With respect you are missing the point. You are not trying to protect a 6mm cable against an overload current with a 100A fuse. By design the circuit cannot be subject to overload. You are trying to protect against a fault current of perhaps a thousand amps and the 100A fuse is likely to do just fine for a 6mm cable. Do the sums.

 

[HandySparks]

spsparks,
While I agree with the others that it may not be best practice, take a look at 433.2.2 and 434.2.1

 

[SolarCity]

To be fair to spsparks I do kind of agree with him.

I saw this for the first time as an apprentice - my college course simplified things by saying "fuse smaller than cable" and letting everything move from there - I saw a guy installing an EPOS system on a shop and using 6mm cable which to my eyes was being supplied by a 100A fuse - and therefore wrong.

I voiced my concerns and was made to look an idiot. Two lessons learnt in one.

My agreement with spsparks is that it just looks like bad practice to me. A pointless short cut.

 

[JD6400]

I too do not see the need to do it , well at least for this size of tails anyway !
I have since found a copy of the regs up here that i had forgot i had spare , and you are right Bruce there does not seem to be a reg against multiple differently sized conductors in a termination .
But having said that i would imagine it may not be following the manufactures instructions for the max csa allowed to be terminated in it ?