solar cowboys report or not

[GaryM]

It's more a case of if you can guarentee a sound reliable mechanical connection with different sized conductors. I'm not sure you could.

 

[yellowvanman]

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.

Don't disagree with all the connections at the breaker, but you are allowed to protect a cable at the 'remote' end as long as the remote end is not too far away!

Read 433.2.

Its been mentioned on this thread before, but you can have 200A busbars and take feeds off the busbar with cable that is a lot smaller current carrying capacity than the 200A device protecting the busbar.

 

[BruceB]

GaryM, The point I was making is that from an electrical protection point of view it is probably OK. Often I find people take awhile to get their mind around the difference between overload protection and fault protection. On the mechanical siode I agree it is a little rough - different size cable can be tricky to fit reliably in a single terminal. I do not know about the present case, but for example MK isolators in CUs can take 50mm2 of cable(s) so it can be achieved with care.

 

[moggy1968]

lets knock this fault current thingy on the head.
Do you replace the cables on a circuit every time the fuse blows, of course not. Do you test them for damage every time the fuse blows, of course not. The only thermal damage that may occur is in the area the short actually occured (i.e where some numbskull has cut the cable, in which case all this is academic anyway, the cables shot!!!)It makes no difference from the point of view of fault protection what size fuse you have. The fault current is the same and the disconnection time is the same regardless of what fuse you put on it. Any cable on any circuit is capable of sustaining that fault current until such time as the protective device operates. It has to be because until it operates the fault current is usually significantly above the rating of any protective device on the circuit.

You are not going to fry a set of 16mm meter tails on a dead short, end of.

The size of the fuse related to the size of the cable is of relevance only in terms of it's current carrying capacity and hence overload protection so in the case cited the cable will not fry and will not be damaged either in the event of a short circuit or overload because of the protective devices employed in the circuit and the maximum demand of the circuits.

 

[Gavin A]

I don't understand why anyone is disagreeing with spssparks here, I can only presume people haven't quite grasped the situation he's explaining.

As I understand it the 6mm cable is connected directly to the suppliers cut off, with only a 100amp suppliers fuse on the supply side to protect it in the event of a short circuit on that cable. The 16mm tails are irrelevant as they're feeding an unrelated 2nd distro board.

No way is this a safe installation, nor is it regs compliant as any cable needs to be protected by a suitably rated over current protection device, and this isn't from the info given unless I'm missing something.

 

[moggy1968]

As above, the total demand doesn't exceed the rating of the cable therefore the level of overcurrent protection os satisfactory as I undersatand the set up. For the reasons I have outlined above fault current isn't really relevant, the fuse will blow without damage to the cable.
Not ideal as a set up for the reasons we've all given but not convinced the problems are as set out by some people here.
It's not something I would do, but I do run 16mm tails from a henley block to supply my PV circuits and see nothing wrong with that (and neither have 2 seperate assessors) and thats kind of the same thing, just not quite so extreme.

 

[dougalthedog]

I think this is one of those situations where the practice probably doesn't meet regulations, but there is little compromise in terms of safety.

Table 4D1A in BS7671 specifies the max current carrying capacity of 6mm as 47A (assuming singles, clipped direct). Regulation 431.1.1 requires the disconnection of a conductor in which an overcurrent is detected. The downstream protection is irrelevant here as it does not disconnect the 6mm conductor.

A current greater than 47A but less than 100A would result in a breach of reg 431.1.1.

However, the circumstances which might lead to this are difficult to imagine. The cables would need to be "shorted" with something having a resistance of a few ohms. As the cables in question are probably pretty short, and in an area you would expect people to be cautious around the risk is reduced further.

I have to admit to having done this with 10mm cables in spite of these not being rated for 100A.

 

[yellowvanman]

As I understand it the 6mm cable is connected directly to the suppliers cut off, with only a 100amp suppliers fuse on the supply side to protect it in the event of a short circuit on that cable. The 16mm tails are irrelevant as they're feeding an unrelated 2nd distro board.

No way is this a safe installation, nor is it regs compliant as any cable needs to be protected by a suitably rated over current protection device, and this isn't from the info given unless I'm missing something.

As I've mentioned previously overcurrent protection can be placed at the 'remote' end of the cable - as per 433.2, so if the 6mm has got a 63A RCD and 2 MCBs of say 32A & 6A, then that sufficiently protects the cable from overload current, max case 38A, which is well below the CCC of 6mm. Fault protection is made by the cutout fuse, and the only thing can can cause that is damage to the 6mm cable.

 

[dougalthedog]

Agreed 433.2.2 would appear to allow this - I stand corrected!

 

[Earthstore]

As I only have a little understanding on this, and smile when all you sparkies quote the regs, you do know your stuff..
Let me ask a simple question on this, as this is the point that I think some are missing; Which is the supply end of this 6mm cable, the 100amp mains fuse, or the 63A RCD with MCB's fitted?

 

[yellowvanman]

As I only have a little understanding on this, and smile when all you sparkies quote the regs, you do know your stuff..
Let me ask a simple question on this, as this is the point that I think some are missing; Which is the supply end of this 6mm cable, the 100amp mains fuse, or the 63A RCD with MCB's fitted?

Supply end is the 100A fuse, and I'll quote another reg:

712.537.2.2.1 ".. the public supply shall be considered the source and the PV installation shall be the load"

 

[blades1898]

Some interesting points here,i personally would use the henley block and meter tails method.Years ago an old gaffer of mine used to tell us to connect the feed of the fire alarm circuits straight into the connection of the meter tails and then to a spur, this would cut the risk of anyone turning it off or tripping out (probably before battery backups were any good). I used to think this was never right but this bloke did know his oinions and have since seen this on many old fire alarms. So basically its the same situation that youve got here. Good Debate.