Loop impedance is 0.55

[greencoat]

hi all,

just had Powersystems reset my prepaymant meter following eviction of a squatter. He then tested the Loop Impedance & said it was too high at 0.55.
He said that the earthing was too small & may need an earth rod too.


Would this mean a complete rewire or could the earthing just be done.


Pete

 

[plugwash]

if an earth supplied by the elecricity supplier is out of spec then its thier problem to sort it not yours.

 

[greencoat]

His note says

" installation unsafe.High loop impedance on earth. Recommend full NICEIC test supply to isolator only. Tails left out due to safety."

He said I'd have to get a spark to come & sort it. Then the spark could just reconnect the tails.

I assumed then it was my responsibility to sort it.



Pete

 

[Steve]

What type of earth is it? Is there an earth wire exiting the supplier's fuse? Can you get a picture? Are there any labels on the suppliers equipment that says "PME"? or something along the lines of "the earth conductor is connected to the main neutral terminal"? Is there an earth wire soldered / clamped onto the main incoming cable?

 

[Spark123]

You can't sort out a supply companies earth problem, the only thing in your control would be to convert to a TT supply. I take it that it must be TN-CS (max 0.35ohms)? TN-S max efli is 0.8 ohms btw. Like pluggy says, ask the DNO to sort it.

 

[securespark]

Where did he test it from?

What system have you?

If he did a Ze, then if it's 0.55, it must be a TN-C-S system.

However, if it's a Ze he's worried about, that's their responsibility to lower it.

If it is a Zs reading, that's not bad, depending of course what type & size the device is.

Some of the higher rated devices (30+A Type C/D & 1361/3036's) need very low readings.

 

[securespark]

Bah!!

At least I wasn't beaten by that southern RCBOphile this time......

 

[greencoat]

Sorry I'm not at the property now.

The supplier's sparky said it was a PME yesterday.

The one who reset the meter today said it may also need an earth rod or that they could use the neutral as an earth, but that would mean calling them out again. ( I waited 4 days for the supply to be switched back on & meter reset).


Pete

 

[securespark]

PME is same as TN-C-S.

In which case he was probably talking about the Ze. (Max 0.35)

The DNO has a responsibility to maintain this earthing facility, as it was provided by them originally. Talk of rods on a PME system is lobbocks!

Ring them up. Tell them they have a duty to rectify their high Ze.

 

[Spark123]

The bit I don't follow though is them saying they may be able to use the neutral as the earth?? If it is PME then the neutral is and the earth are combined anyway?

 

[greencoat]

I saw 2 earth cables when I looked in the meter cupboard. It must have been from the cu to the earth block and some bonding maybe?
After the test,The spark said it was too small, around 4sqmm and that it should be bigger, maybe 10. Then he said about getting it seen to.

I was upstairs when he tested so I don't know where he did it.

If those earths are too small, is that the cause of the problem or just another part of it?

Cheers,

pete

 

[Spark123]

Depending on the supply type, the connection between the DNO knockout and the MET (main earth terminal) on a normal 100A supply with 35mm² tails is normally 16mm² -you may need to get DNO to do this. The main CPC from the MET to the consumer unit is normally 16mm². The main equipotential bonding from the MET to water main, gas main etc is normally 10mm² although in the case of PME the DNO can overrule this and say these need to be 16mm². (These sizes also depend on the cables length (hence resistance) not exceeding 0.05ohms.)

 

[greencoat]

Thanks for replies.

I'll just have to have a much closer look in the daylight. ( Sod's law that I'm on nights.)

Pete



Ps can't believe that s0d's law was edited!

 

[securespark]

Depending on the supply type, the connection between the DNO knockout and the MET (main earth terminal) on a normal 100A supply with 35mm² tails is normally 16mm² -you may need to get DNO to do this.

Sometimes, the screws or allen grubs are exposed, and you can connect a piece of 16 milli yourself, should you wish to.

 

[RF Lighting]

You need to be careful with this though.

The 'earth' block on this cutout is not actually connected to earth (or earthed neutral)