What supply type is this?

[RF Lighting]

Came across this supply today. Ze is 0.46Ω

 

[dingodeano]

Tn-c-s-c.

 

[westie101]

Without removing the cover on L3/neutral/earth hard to say as all of them have separate connector blocks, to PME it would need the N/E link inserted.
I'm also a bit suspicious of the "clamps" on the armour & sheath as they are not common in these parts except as a temporary fix or non DNO fit

 

[RF Lighting]

I suppose it could be a link just to provide an earth to the earth terminal on the top of the cutout. I never thought to take a line to neutral loop whilst I was there. I wasn't quite firing on all cylinders today

The Ze and lack of PME notice suggests TN-S to me.

I have been to a job years ago where the main earth was connected to that terminal, but the suppliers earth was an unused clamp on the cable sheath. Obviously had never been tested!

Those clamps are standard round here. They are replaced with constant force springs if the DNO works on the supply, but 90% of PILC supplies round here have those exact clamps.

 

[westie101]

Yes I think the confusion is incorrectly taking the G/Y earth from the armour clamp rather than correctly the available earth connection on the cut-out.

The standard here would see the armour & sheath sweated together and an earth wire also included, we are also using "roll" springs now on all sheath to earth wire connections

 

[ericmark]

OK it's a TN supply does it really matter if TN-S which would seem most likely or TN-C-S remembering if the neutral and earth are combined anywhere other than the substation it is a TN-C-S.

Petrol stations, caravan sites, and mariners need a TN-S or TT but for the rest does it really matter?

OK I know paperwork asks for supply type but is there any reason why we should not just enter TN.

 

[RF Lighting]

It doesn't really matter for this particular installation. I was just trying to keep my paperwork accurate, and also to verify the Ze is within the permitted values which it is for TN-S but not for TN-C-S.

 

[westie101]

but not for TN-C-S.

Ah but it is!

The figure of .35 is from a Supply Industry specification going back to the '60s! .35 was a guestimate at the time as it was reasoned that in most cases it would be lower than the .8 figure for TN-s as the neutral and earth were combined.
This figure was included in the regs but only by permission of the supply industry.

But what does the figure actually mean? That a 100A cut out fuse will operate within 5s for a live to neutral or earth fault prior to the first set of customer protective devices.

From one of our documents

2.1 ENA Engineering Recommendation P23/1 gives Guidance relating to Consumers Earth Fault Protection and advice required from Public Electricity Supply Companies.

2.2 Within this document are published suggested maximum values of Earth Loop Impedance (ELI),
primarily for use as a guide to designers of private installations for consideration of their protective devices. The ELI values should allow the service termination fuse to operate within 5s in line with BS7671 and CPxxx.

2.3 In line with these suggested guidance notes **** has adopted the following figures as acceptable values of ELI to be measured at the incoming service termination where an earth terminal has been provided
Non PME System = 0.8 ohm
PME System = 0.35 ohm
(Higher values can be accepted up to 0.8 ohm)
(The value for a PME system being lower as to be expected with the combined neutral / earth configuration)

So .35/.8 is not cast in stone and should be treated as such. We can accept higher values than .8 on a temporary basis by reducing fuse size or ensuring an RCD is fitted immediately after the cutout whilst the situation is rectified

 

[17thman]

but not for TN-C-S.

Ah but it is!

The figure of .35 is from a Supply Industry specification going back to the '60s! .35 was a guestimate at the time as it was reasoned that in most cases it would be lower than the .8 figure for TN-s as the neutral and earth were combined.
This figure was included in the regs but only by permission of the supply industry.

But what does the figure actually mean? That a 100A cut out fuse will operate within 5s for a live to neutral or earth fault prior to the first set of customer protective devices.

From one of our documents

2.1 ENA Engineering Recommendation P23/1 gives Guidance relating to Consumers Earth Fault Protection and advice required from Public Electricity Supply Companies.

2.2 Within this document are published suggested maximum values of Earth Loop Impedance (ELI),
primarily for use as a guide to designers of private installations for consideration of their protective devices. The ELI values should allow the service termination fuse to operate within 5s in line with BS7671 and CPxxx.

2.3 In line with these suggested guidance notes **** has adopted the following figures as acceptable values of ELI to be measured at the incoming service termination where an earth terminal has been provided
Non PME System = 0.8 ohm
PME System = 0.35 ohm
(Higher values can be accepted up to 0.8 ohm)
(The value for a PME system being lower as to be expected with the combined neutral / earth configuration)

So .35/.8 is not cast in stone and should be treated as such. We can accept higher values than .8 on a temporary basis by reducing fuse size or ensuring an RCD is fitted immediately after the cutout whilst the situation is rectified

this is true. 0.35 ohms is only a typical value for a pme supply

 

[dinopower]

here in north devon, when the dno used that type of clamp it was soldered on top, later clamps where steel henley clamp and now using roll springs, although a lot of electricians have put those clamps on and called us when the z's where high, only to have the clamp taken off because earth not available, typicly because old dc cables with iron clamp type joints,(lead sheath not soldered, just relying on cast iron clamps

 

[studentspark]

I never thought to take a line to neutral loop whilst I was there.

Could you expand on the line to neutral loop test please

Thanks

 

[JohnW2]

Could you expand on the line to neutral loop test please

Exactly the same as the standard line-to-earth loop impedance test (i.e. Earth Fault Loop Impedance), but with the test 'short' applied between line and neutral (rather than between line and earth) - i.e. a L-N fault Loop Impedence.

Kind Regards, John

 

[EFLImpudence]

Could you expand on the line to neutral loop test please

This L-N will give you the PSCC as L-E gives you PEFC.

The greater of which is the PFC.

 

[JohnW2]

Could you expand on the line to neutral loop test please

This L-N will give you the PSCC as L-E gives you PEFC. The greater of which is the PFC.

In the absence of supply-side faults, do you ever see PEFC>PSCC?

Kind Regards, John

 

[EFLImpudence]

Only with a huge earthing conductor on TNC-S but then it's not much.

No I haven't but that's how it's worded.


Did I read recently where it could be or am I thinking of something else?