main connection to consumer unit or meter tails

[marc8]

hi all
been fitting immersuns for a while now & whilst installing one the other day found that 2.5T/E

been placed inside main consumer unit with tails at point of entry to main switch, seen this twice now in last
couple of months. have the regs changed that you can feed another isolator from mains with 2.5T/E without
going through a Fuse/Cb first or is this just acceptable for solar pv as fairly new to solar myself just thought
i would ask, if i installed this during my normal day at end of year i would get pulled for it?

 

[SPARTYKUS]

No its not okay because the 2.5mm2 twin and earth will melt / catch fire a long time before the main fuse goes. So the circuit is a fuse (or bomb, depends how you look at it)

 

[marc8]

hi spartykus
customer was well proud of their install i did not mention, not my place really.
but if you have to belong to MCS & alike i thought they would be hot on this sort of thing

 

[SPARTYKUS]

You'd think so!

 

[Gavin A]

The argument for being allowed to do this goes that it's a current limiited device, and according to BGB it's allowed to run a circuit for a current limited device without overload protection, and the suppliers fuse would supply fault protection.

So by that reading of the regs, it would seem to be allowed, however G83 specifies seperate overload protection for the circuit, so it's actually not allowed for solar PV installed under G83 or G59.... so basically all grid connect solar PV, as the DNO don't want anyone to be using their fuse as the only fault protection on the circuit whether it's current limited or not.

so no it's not allowed, the installers doing it are breaking G83 regulations and therefore the system doesn't have permission to connect to the grid

 

[telectrix]

every day i learn more about solar. by time i'm 70, think i might just know enough. ( shut up , geordie!. :rofl: ). :tounge_smile:

 

[marc8]

hi Gavin
i have seen it a couple of times mainly when fuse box is old & no spare ways as reading all through your notes would have been easy solution if it was allowed but thought i would ask first cheers

 

[BruceB]

So by that reading of the regs, it would seem to be allowed, however G83 specifies seperate overload protection for the circuit, so it's actually not allowed for solar PV installed under G83 or G59.... so basically all grid connect solar PV, as the DNO don't want anyone to be using their fuse as the only fault protection on the circuit whether it's current limited or not.

so no it's not allowed, the installers doing it are breaking G83 regulations and therefore the system doesn't have permission to connect to the grid

Have you got the reference for that, so I can read it? The downstream PV mcb will be providing overload protection separate from the DNO fuse.

 

[puddy]

Can you condemn the fuse box? The same way an unsafe gas appliance would be condemned or do uninstall the circuit to make it safe or walk after telling the client?

I am not an electrician just a homeowner with solar

 

[AndyL]

The argument for being allowed to do this goes that it's a current limiited device, and according to BGB it's allowed to run a circuit for a current limited device without overload protection, and the suppliers fuse would supply fault protection.

So by that reading of the regs, it would seem to be allowed, however G83 specifies seperate overload protection for the circuit, so it's actually not allowed for solar PV installed under G83 or G59.... so basically all grid connect solar PV, as the DNO don't want anyone to be using their fuse as the only fault protection on the circuit whether it's current limited or not.

so no it's not allowed, the installers doing it are breaking G83 regulations and therefore the system doesn't have permission to connect to the grid

The 100A fuse may not give fault protection either to a 2.5mm cable

 

[JulianC]

Does the 2.5mm out of the main switch feed in to an MCB in a dedicated consumer unit for the PV circuit? If it does then overload and fault protection might be OK, despite the out-and-out shoddiness of the execution. If no MCB then there's a problem. As AndyL says, 100A fuse won't provide fault protection.

 

[marc8]

hi
the 2.5mm does go to a consumer up the wall so there is a 16cb at that point, which provides 16amps for the cable
to the inverter / ac isolator.
but am sure that should only change size of cable after going through overcurrent protective device otherwise
cable is not rated for fusing.

 

[Gavin A]

Have you got the reference for that, so I can read it? The downstream PV mcb will be providing overload protection separate from the DNO fuse.

I was working on the basis that there wasn't an MCB at all, but might have misunderstood.

the reference is the G83/2 engineering document, not sure which page as I'm working from memory.

 

[Gavin A]

The 100A fuse may not give fault protection either to a 2.5mm cable

probably right, I considered it as an option for 6mm2 on a job a while back before ruling it out after checking the G83 regs. I stopped at that point so didn't do those calcs to check that side of things.

Twas a thread elsewhere on here that prompted me to investigate it

 

[Gavin A]

hi Gavin
i have seen it a couple of times mainly when fuse box is old & no spare ways as reading all through your notes would have been easy solution if it was allowed but thought i would ask first cheers

henley block on the tails, though you're then into the issue of safe isolation.

 

[BruceB]

I had a look at g83/2 and thought it was sufficiently vague that provided:
- there is a downstream mcb to provide overload protection
- the prospective fault current at the downstream mcb was enough to blow the suppliers fuse
then it meets g83/2 and 7671.

But there is a serious risk that a single 2.5mm conductor will not be gripped properly in the input terminals of a standard cu main switch when alongside say a 25mm conductor

 

[wersolaruk]

This really is very bad practise the tails should been spilit through a double pole Henley block which then feeds a 1 way rcd protected or main switch depending upon cable routing and mechanical protection, the circuit would then be fed from 2.5 t+e 16a mcb, this really boils my wee when a total lack of experience or being under pressure to complete job and you have not got a Henley block or tails just sheer laziness in my book. But the customer does not have a clue, would be due to in correct survey.

 

[SPARTYKUS]

I don't understand why this could possibly be argued to be okay.... In the event of a fault (short circuit, overload) the cable will fry. Which bit am I missing?

a solar course?

I understand it is not a normal cable as per a normal CU, in that it is feeding back but it could still, conceivably, by a long shot, be the subject of trauma.

I'm not having a dig, just want to follow

 

[Gavin A]

I don't understand why this could possibly be argued to be okay.... In the event of a fault (short circuit, overload) the cable will fry. Which bit am I missing?

it's a current limited device, so can't possibly overload a correctly sized cable outside of fault conditions (reg 433.3.1 (ii) I think)

the fault current is really the issue here, where in some circumstances the bullet could supply sufficient protection against fault currents (probably not the case with 2.5mm cable, as pointed out above), but the DNO don't allow this as per the G83 regs.

For clarity, I don't think anyone's saying it's ok or good practice, I'm just outlining what the thinking is behind it, and why some sparks might think that it could be allowed if they'd not spotted the line about this in the G83 regs.

 

[Gavin A]

manufacturers instructions would also come in here, as most specify the maximum overload protection device allowed for that inverter.

 

[SolarCity]

I don't understand why this could possibly be argued to be okay.... In the event of a fault (short circuit, overload) the cable will fry. Which bit am I missing?

a solar course?

I understand it is not a normal cable as per a normal CU, in that it is feeding back but it could still, conceivably, by a long shot, be the subject of trauma.

I'm not having a dig, just want to follow

The cable won't fry. The fuse will blow in the event of short circuit.

However, I think most of us would agree that it is very bad practice. As BruceB says, 2.5 in a connection with 16/25mm is incorrect anyway but even so, why not just do the job properly?

 

[Gavin A]

The cable won't fry. The fuse will blow in the event of short circuit.

However, I think most of us would agree that it is very bad practice. As BruceB says, 2.5 in a connection with 16/25mm is incorrect anyway but even so, why not just do the job properly?

yep - it's not as if the customer's paying several thousand pounds for the installation is it... no wait, that's exactly what they're doing, so saving £50 max on a proper garage unit, henley block and tails is taking the **** really.