pnb

[maguire]

Hi Guys
Anyone know what the max Ze is for a pnb system and how can I tell if this is in fact the earthing system employed, at present there are two earth rods at the property and readings indicate a TT set up but DNO say its PNB
Mac

 

[GaryMo]

Do you mean PME? If so then 0.35ohms.

If your DNO says it's PME then it's PME. They're the people who know the network.

 

[dingbat]

Hi Guys
Anyone know what the max Ze is for a pnb system and how can I tell if this is in fact the earthing system employed, at present there are two earth rods at the property and readings indicate a TT set up but DNO say its PNB
Mac

PNB is form of TN-C-S. You should connect your installation's MET to the earthed neutral (PEN) conductor at the transformer earth electrode and get a max of 0.35 Ohms. (Check with the distributor again.)

If you are earthing your installation to a separate earth electrode, then you are making it a TT system and it is down to you to get a Ze of (max) 200 Ohms, preferably much lower.

 

[GaryMo]

I guess you learn something new everyday. I hadn't heard of PNB.

PNB Earthing

PNB is a special method of earthing, similar to PME, where the neutral earth is installed at or adjacent to the customer’s installation instead of at the transformer position. This method can still be used provided the supply is from a dedicated pole mounted transformer supplying a single customer.

 

[dingbat]

I guess you learn something new everyday. I hadn't heard of PNB.

Happy to help.

 

[GaryMo]

Happy to help.

Is that better?

 

[Guitarguy]

ah PNB, can be very dangerous if there's little known about it- i.e if the earth connection is broken/removed, the neutral/ earth will become live as that's what's holding the voltage down at the transformer. If say, someone is digging and hits the earth wire off the earth rod and thinks 'oops, i'll just reconnect it.' The moment they touch the wire they will electrocuted