Radial Circuit in Garage - Change to Ring?

[securespark]

Is it two core SWA?

Do you have any buried metallic water pipes in the garage?

What is your supply type?

 

[crappy]

Is it two core SWA?

Yes, direct buried.

What is your supply type?

He drives an old mondeo... Sorry, wrong group.
Normal single phase into house, then through 40A mcb into garage cu.

Do you have any buried metallic water pipes in the garage?

Yes but I suspect its fed from blue plastic pipe from house. Not metal all the way. The tap goes into poured concrete so cannot tell how much is actually in contact with earth.

 

[EFLImpudence]

Garage is fed from house, 6mm buried armoured. Mcb in house is 42A and feeds a CU with earth leakage device.

There are no 42A MCBs. Do you mean 32A?

At the risk of prolonging the very interesting dialogue, there is no - that I can see - earth spike in the garage which is about 50m away.

That could be fine.

Obviously the armoured has the armour which is earth but is that all that is needed?

Could be.
Not possible to tell on the internet nor by looking at it.
Test measurements need to be taken.

You don't have to earth outbuildings?

The garage installation will obviously be earthed by the house installation.

Risk of some odd ground loops if you do?

SS will have meant what method of earthing is used for the house supply.

 

[EFLImpudence]

Normal single phase into house, then through 40A mcb into garage cu.

Ah 40A - ok.

Yes but I suspect its fed from blue plastic pipe from house. Not metal all the way. The tap goes into poured concrete so cannot tell how much is actually in contact with earth.

Metal pipe would have been better. Can you make sure?

Is the tap pipe bonded to the garage consumer unit?

As I said, it needs testing to determine if all is well.

 

[crappy]

I'll double check the garage cu but cannot recall.

 

[EFLImpudence]

Is the tap pipe bonded to the garage consumer unit?

Just to clarify - I'm not saying it should be (although if it contacts the ground it likely should be - another test measurement) just asking if it is.

 

[ericmark]

2.5hp compressor

1 hp approx = 750 watt so around just under 2 kW run start = approx 10 times run, so 20 kW, approx 86 amp, although for a small time. So at 50 meters looking at a volt drop of around 45 volt.

Rather approximate as clearly some compressor will need more starting than others, using an inverter drive you could reduce the start load by a huge amount, but compressors are not easy, as they need de-loading. And at 45 volt drop likely will stall.

 

[Harry Bloomfield]

1 hp approx = 750 watt so around just under 2 kW run start = approx 10 times run, so 20 kW, approx 86 amp, although for a small time. So at 50 meters looking at a volt drop of around 45 volt.

Don't most compressors include an unloader valve, so they start without the compression load? Mine does, so motor will be starting without any real mechanical load.

 

[SUNRAY]

That's not quite what I said. BS7671 has a reasonable amount say about conductors in parallel in general, particularly in relation to their protection against overcurrent.

The issue to which I was referring is that a circuit such as I mentioned does not appear (as 'guidance') as one of the examples of final sockets circuits given in Appendix 15 of BS7671 - and 'those with limited ability to think' seem to assume that anything which does not appear in that guidance is 'not permitted'. Another example of that is a 4mm² unfused spur from a ring final.
Kind Regards, John

Thanks

Why do you 'understand the hesitancy' - just because it is 'unfamiliar', perhaps? Whether there would often be any particularly good reason for wanting such a hypothetical "50A radial" is a different matter - two 32A/4mm² radials (or two 32A/2.5mm² ring finals) would presumably usually what would be used.

Kind Regards, John

I have seen various 'unusual' circuit designs over the years and I'll absolutely and totally expect EICR % fails of this sort of circuit:

to be into the high 90's.
It will invariably be described a a ring with one socket and 3 sockets on a spur, or a ring with forbidden links etc.
You know and I know it's fully compliant but I imagine some of the regular good posters on here may struggle with accepting it. Not least of which may be due to the difficulty of getting 4x 2.5mm² T&E's into a BS1363 acceessory or even the backbox.

 

[EFLImpudence]

If you are correct, then it just shows the abysmal quality of EICR inspectors.

 

[SUNRAY]

If you are correct, then it just shows the abysmal quality of EICR inspectors.

 

[EFLImpudence]

I don't have any here so would someone please be kind enough to tell me the diameter of socket terminals?

 

[SUNRAY]

I don't have any here so would someone please be kind enough to tell me the diameter of socket terminals?

Varies from make to make and year to year.
3x 2.5mm² solid is fine and generally 4x 2.5mm² solid is doable but not always and 5x 2.5mm² solid is not doable.

I still have some NOS Bill DSO's which easily accept 5x 2.5mm² solid and 6x 2.5mm² solid at a squeeze. However 2x 2.5mm² solid needs doubling over to be secure.

 

[Harry Bloomfield]

Thanks
I have seen various 'unusual' circuit designs over the years and I'll absolutely and totally expect EICR % fails of this sort of circuit:
View attachment 258885to be into the high 90's.
It will invariably be described a a ring with one socket and 3 sockets on a spur, or a ring with forbidden links etc.
You know and I know it's fully compliant but I imagine some of the regular good posters on here may struggle with accepting it. Not least of which may be due to the difficulty of getting 4x 2.5mm² T&E's into a BS1363 acceessory or even the backbox.

I would do it - CU > S1 > S3 > S4 > S2 > CU. It is then reasonably balanced. Better would be five sockets as in CU > S1 > S3 > S5 > S4 > S2 > CU

 

[SUNRAY]

I would do it - CU > S1 > S3 > S4 > S2 > CU. It is then reasonably balanced. Better would be five sockets as in CU > S1 > S3 > S5 > S4 > S2 > CU

I most probably would too but this sub threadlette is about wiring a 32A or even a 50A radial... using parallel feed 2.5mm² cable.