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Metal - clad buildings and the confused forum member.

One of the members has queried ESQCR bonding/earthing PME requirements for the above. So its worth spending a little time putting across the companies requirements. Where metal-clad buildings incorporate a steel-frame that utilises steel vertical beams that are within the foundations, the steel frame will provide a good connection with the earth which will effectively limit the earth potential rise.

A PME service may be provided to a metal-clad building provided the following criteria are satisfied:

1. The metal cladding is bonded to the steel-frame.

2. The supply is either three-phase with less than 40% unbalance or the supply is single - phase and the frame to earth impedance is les than 20ohms.

Regards, UKPN?

0 Former Community Member over 4 years ago

UKPN:

One of the members has queried ESQCR bonding/earthing PME requirements for the above. So its worth spending a little time putting across the companies requirements. Where metal-clad buildings incorporate a steel-frame that utilises steel vertical beams that are within the foundations, the steel frame will provide a good connection with the earth which will effectively limit the earth potential rise.

A PME service may be provided to a metal-clad building provided the following criteria are satisfied:

1. The metal cladding is bonded to the steel-frame.

Thanks UKPN, out of interest, how do you recommend bonding thin plastic coated metal sheets to a steel frame?
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0 ebee over 4 years ago

Well UKPN did refer to "The confused Forum Member".

I gather that he likes to lob a hand grenade in from time to time

Hmm I might be on wrong thread here rather than one with a similar title. Guess that`s me confused then!
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0 Former Community Member over 4 years ago

A PME service may be provided to a metal-clad building provided the following criteria are satisfied:

1. The metal cladding is bonded to the steel-frame.

2. The supply is either three-phase with less than 40% unbalance or the supply is single - phase and the frame to earth impedance is les than 20ohms.

3? The building has only ONE service connected, if more than one service is required due to the building being split into individual units (terrace like), those subsequent services can only be TT?

True or false?

Regards

BOD
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0 Alan Capon over 4 years ago

I would say true, unless all the services are provided to a common point, with all the meters at that same location.

Regards,

Alan.
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0 AJJewsbury over 4 years ago

I understood that some DNOs at least are now happy to provide multiple units in a steel framed structure with individual PME supplies - but with the proviso that the individual premises are supplied via SNE cables from a common point.

The last point does rather beg the question why if 20 Ohms is good enough for single phase installations, why it's not also good for 3-phase installations with 40% or more imbalance.

- Andy.
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0 OlympusMons over 4 years ago

point 2 could be read either ((3P+<40%unbalance OR SP) AND (Z<20Ohms)), or ((3P+<40%unbalance) OR (SP AND Z<20Ohms))

It could be clearer, but thanks for sharing UKPN
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0 Sparkingchip over 4 years ago

I stand looking at installations and end up up with so many questions in my head.
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0 gkenyon over 4 years ago

perspicacious:
A PME service may be provided to a metal-clad building provided the following criteria are satisfied:

1. The metal cladding is bonded to the steel-frame.

2. The supply is either three-phase with less than 40% unbalance or the supply is single - phase and the frame to earth impedance is les than 20ohms.

3? The building has only ONE service connected, if more than one service is required due to the building being split into individual units (terrace like), those subsequent services can only be TT?

True or false?

Regards

BOD

That's very interesting ... how is the TT installation immediately adjacent to the PME supplied installation separated from the PME earthing system?

If the answer is "it doesn't matter" (from the DNO perspective), and the TT earthing arrangement is not properly separated, then we are in a tricky situation in cases where the PME earthing system is not connected to the HV earthing system at the supply transformer, as the statement U_f = 0 in Table 44.1 of BS 7671 is no longer always true !
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0 Alan Capon over 4 years ago

gkenyon:

That's very interesting ... how is the TT installation immediately adjacent to the PME supplied installation separated from the PME earthing system?

For us, the issue would be two or more PME services into different areas of a steel building. It would be possible for the steelwork of the building to carry diverted neutral currents, for which it almost certainly would not be rated.

Regards,

Alan.
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0 Chris Pearson over 4 years ago

Alan Capon:
gkenyon:

That's very interesting ... how is the TT installation immediately adjacent to the PME supplied installation separated from the PME earthing system?

For us, the issue would be two or more PME services into different areas of a steel building. It would be possible for the steelwork of the building to carry diverted neutral currents, for which it almost certainly would not be rated.

So what is the solution - there must be plenty of light industrial estates with units under a common roof?

Interconnect the METs so that any diverted neutral currents go by a known path?

Separate N and PE on entry to the building and distribute to each unit (with its own meter)?
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Metal - clad buildings and the confused forum member.

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