Hi Ze & Pfc

[Jel]

Hi,

I was testing 2 shops today. One had 2 x single phase CU's & one had 1 single phase CU, all supplied from the basement which had the 3 phases down there.
On one board the reading i got were all fine, but the other 2 i had a reading of Ze: 4.61 and Pfc: 59A. This is very high which means a lot of my circuits will fail on the Ze, but are ok for R1+R2. Anyone got any suggestions, as to why it maybe be so high?

 

[Guest123]

Did you test R1+R2 of the sub-main supplying this DB??

Just to be clear, an installation has only one Ze, at the origin. What you have measured is the Zs of the sub-main circuit, AKA Zdb.

 

[Jel]

Yes sorry, but why would the Zdb be so high, if it so close to the mains?

 

[Guest123]

Yes sorry, but why would the Zdb be so high, if it so close to the mains?

If Ze was fine but Zs at the sub DB was not, this indicates a problem with the sub-main cable.

What was the R1+R2 reading for the sub-main???

 

[Jel]

I didn't have a R1+R2 of the board, i did one for each circuit, and did a Ze and Pfc of the board.

 

[SirKit Breaker]

As lenny has said if Ze is fine, and your Zs (Zdb) at each sub board is dodgy, then you need to give your submains a real good coat of looking at. How is the earth cable terminated? is it onto a rusty old nut and bolt? I have seen some nasty stuff but, you will be surprised at how little corrosion or very slightly loose connections can have a massive impact on your test results.

Cheers............Howard

 

[Jel]

Yeah i could try that.
Oh and they are not sub mains, they are all connected directly to the mains.

 

[stuart569]

I had one with a sub board.SWA to a 100amp isolator.using the armour as earth they had banjo'd the SWA to the isolator and stuck a bolt and nut in.Took the earth from the board on to a supplied bolt on side of Isolator for Earth.Never put a loop between so we got pants loop imp readings!

 

[flyingsparky]

As Sirkit Breaker states, even the slightest corrosion will cause huge problems. You basically have no earth at those boards. If you are only doing a PIR, its technically not down to you to repair, but, it would have been a great time to issue a danger notice to the client or end user and strongly suggest that they allow you to investigate further.

 

[IQ Electrical]

Hi,

I was testing 2 shops today. One had 2 x single phase CU's & one had 1 single phase CU, all supplied from the basement which had the 3 phases down there.
On one board the reading i got were all fine, but the other 2 i had a reading of Ze: 4.61 and Pfc: 59A. This is very high which means a lot of my circuits will fail on the Ze, but are ok for R1+R2. Anyone got any suggestions, as to why it maybe be so high?

The poor earth seems likely but I don't suppose there was a UPS supplying this suspect consumer unit (maybe for tills etc.)?

 

[Jel]

The poor earth seems likely but I don't suppose there was a UPS supplying this suspect consumer unit (maybe for tills etc.)?

No no UPS.
Will back and check all the connections.