solar cowboys report or not

[spsparks]

100A Square D QOE Isolator on dist board with 25mm tails from service head (100A), then a 16mm sharing the incoming side of the isolator to a 2nd DB.

The dummy then sticks a 6mm2 in along with them to a 63A RCCB for solar DB......... NICEIC reg. company apparently.
Guess he couldnt fit another 25mm in there. Only wish I had taken a photo.

 

[Earthstore]

The experts will answer this I dare say.
Depending on the size of the PV system, and the length of the AC run, a 6mm cable sounds fine (has to have <1% drop) as the PV circuit should not be on a shared circuit.
Unless the system is mounted in another building, or has a long cable run, you would never need 25mm cable.
Of course, how he made the connection, only you have seen that, by the sounds of things it could have been better.
And you are right a photo would have been good.

I hope this helps.

 

[spsparks]

dont think you got the gist of this ..........service fuse 100A then 6mm to 63A rccb in shared terminal with 25mm tails and 16mm tails. No suitable overcurrent protection on 6mm cable IMHO
What happens if there is a fault on 6mm ?..........

 

[GaryM]

6mm2 is probably fine supplying a 1 way CU with a maximum demand of 16A.
What isn't fine is a 25, 16 and 6mm conductor in the same terminal. There's no way you can guarantee a sound mechanical connection.

What kind of fault on the 6mm?

Imagine a 400A busbar chamber supplying multiple 63A isolators. Are you suggesting all supplying conductors to the isolators should be capable of carrying 400A?

 

[Earthstore]

I am not a sparky, I do not work on electrical systems, but I do understand PV systems, so just trying to help.
I think I understand what you are saying now about the overcurrent protection for the 6mm.
But as a pv system is a supply,and a dedicated circuit, with a maximum output (normally 3.68KW on a domestic installation) and the grid voltage is regulated, there is no possibility of overcurrent, unless as you say the 6mm cable goes faulty.
So, not too sure, one of the experts will be on here later, and probably tell you which reg applies.

Just trying to help.

 

[spsparks]

We are not discussing the merits of 3 phase distribution. But are discussing a single phase situation that COULD lead to a dangerous situation and doesnt comply with Regs. It was signed of by an NICEIC reg. company.
As I said it runs to a 63A RCCB from the isolator. Two mcbs 16A and a 6A in small CU............but thats a minor detail.

BS7671 chapter 43 and best practice guide 3.
I wonder what supplier would say to a 6mm being run from their service fuse.

 

[GaryM]

I wonder what supplier would say to a 6mm being run from their service fuse.

Nothing, if all it feeds is a 2 way consumer unit with a 16A and 6A circuit.
You need to understand that the main fuse protects the cable coming in from the street, not the consumers installation.

What's the danger to the 6mm conductors in this instance?

 

[spsparks]

I appreciate the feed back Earthstore. I also understand that practically their is unlikely to be a problem with the cable. If this is the way these systems are being installed then they dont comply with regs requirements for protection from over current. I will ask the supplier what tails they spec (usually 25mm). As this is an indirect connection to these. I think its a poor quality job when the solution is to use a couple of 3 way 100A JBs and run 25mm tails to the RCCB. That does comply with regs and would be a better solution. I reckon he used 6mm as it was all he could get in the terminal.

 

[spsparks]

You need to understand that the main fuse protects the cable coming in from the street, not the consumers installation.

What's the danger to the 6mm conductors in this instance?

Then to that logic you are using a 63A RCCB to protect a 6mm cable ????

 

[GaryM]

If this is the way these systems are being installed then they dont comply with regs requirements for protection from over current. I will ask the supplier what tails they spec (usually 25mm).

Why doesnt it comply with overcurrent requirements? Have you got a direct link to a regulation? Bet you don't find one!
Why would the DNO be interested?

I've seen many 1 way CU's supplying showers with 6mm2 DI tails from a henley block. Nothing at all wrong with them.

 

[GaryM]

Then to that logic you are using a 63A RCCB to protect a 6mm cable ????

Nope, the circuit breakers combined will have a maximum demand of 22A. An RCCB won't provide overcurrent protection.

 

[spsparks]

You obviously cant be bothered to look for yourself and based on your reponses that doesnt surprise me.
433.1.1 (ii) but many more in the whole section you should read.

 

[GaryM]

Will have a look. It's not that I can't be bothered, it's just that I think you're wrong. No offence intended so lets keep it to a friendly debate.

 

[GaryM]

Just looked. You don't agree that two protective devices - 16A and 6A won't offer protection against overload of a 6mm2 conductor? Don't you think either will trip if their respective circuits generate more than 16A or 6A for a long duration?

 

[JD6400]

Not done the calcs yet as the weekend and all the books are at the office , 6mm on a 63amp breaker sounds to large at the moment and as for squeezing them all into the incoming side of the main switch instead of a Henley block is just plain and simple rough as a Brock let alone any of the regs that i am sure you would find that just simply say NO ! I would hope ?
But there is absolutely no reason not to use the 6mm if it is covered by a appropriate protective devise on the incoming load side ? (To limit the load draw down the 6 mm )
I hope that last bit made sense .

 

[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?