Earth Loop Impedance Test and problem with power supply

[Maverick777]

Hi,

Our main fuse from the power distributor blew and Western Power attended and replaced. During this visit they established that their was a problem with reverse polarity and that when the RCD was installed the tails in the grey twin cable were connected red-black in the top of the consumer unit.This particular type of unit needs to be black-red. It is probable that we removed the external fuse to enable the RCD to be installed and on completion the fuse was replaced. However polarity checks showed reverse polarity.To correct this the tails were reversed on top of the external cut-out and this cured the problem. At this stage there was no electrical danger and it stayed that way until the shower developed a fault last week and the crossed tails were spotted.

I've had an electrician attend who spent all day testing and the Earth Loop Impedance Test showed a reading of 363 Ohms which I believe is very high. He has recommended changing the circuit board at a cost £350.00. However this does not gurantee that the problem will be resolved. Please advise.

Thanks

 

[Plonker 3]

Has he given you any sort of paperwork?

I take it you mean he took the Ze or external loop impedance at your distribution board.

It sounds like it could be a TT system where the DNO doesn't supply an earth but it is provided locally via a earth rod. If that is the case then putting new earth rods in until the readings are satisfactory is the best solution.

If it is either a TN-C-S or a TN-C then it is the distributors responsibility to proved the earth in which case contact them.

As for the reverse polarity has that been resolved with a certificate issued?

 

[Paul.M]

Apart from the reverse polarity has the electrician said why you need a board change?

 

[Geordie Spark]

Apart from the reverse polarity has the electrician said why you need a board change?

KERCHING !!!!!!!!!!! perhaps?

 

[Paul.M]

KERCHING !!!!!!!!!!! perhaps?

I didn't want to insinuate that it came down to money without knowing all the facts but KERCHING is the odds on favourite.

 

[Engineer54]

One things for absolute sure, ...A board chance isn't going to solve the high Zs value!!
As already been suggested, this is in all likelihood a TT system that has been badly installed in the first place. Having said that, is there any bonding to the main water/gas services in place??

I'm going to make an assumptions now!! ....I wouldn't expect such a high Zs with both of these services being bonded back to the MET, which means you ''Don't have'' any bonding in place!!

Your living very dangerously on the edge there i'm afraid, and totally relying on a single RCD device. I'd get your electrician back, and start asking him some very relevant questions, ....Like did you not notice i have no bonding conductors to my main water and gas services. And what is the Ze of my installation...lol!!! Those high Zs values should have rang alarm bells, and should have led him, to be checking main earthing and bonding conductors, before talking about CU changes!!

If my assumption is correct, then i would seriously be thinking about a change of electrician, one that has a good reputation in your area.... lol!!

 

[Plonker 3]

I've had an electrician attend who spent all day testing and the Earth Loop Impedance Test showed a reading of 363 Ohms which I believe is very high. He has recommended changing the circuit board at a cost £350.00. However this does not gurantee that the problem will be resolved. Please advise.

Thanks

How does a new DB bring down the earth loop results?

 

[ACDC]

How does a new DB bring down the earth loop results?

It wont. (I assume your DB has RCD(s) installed by your op)

 

[Engineer54]

I've had an electrician attend who spent all day testing and the Earth Loop Impedance Test showed a reading of 363 Ohms which I believe is very high. He has recommended changing the circuit board at a cost £350.00. However this does not gurantee that the problem will be resolved. Please advise.
Thanks

Any chance of you posting a photo or two of your CU (front cover removed), and the supply cut-out?? This will give us all a much better understanding of what you have or don't have, and enable us to give, as is the best advise on how to proceed!!

My earlier post maybe totally wrong, but i don't think so, not going by that enormous 363 ohm value you have quoted!! lol!!

 

[Maverick777]

Hi,

Thanks one and all for your replies. I'm no expert, not even a good DIY'er. However having listened to the power distributors that attended (Western Power = WP) following the original power failure it would seem that whoever put the power into the house from the grid, put the wires in, the wrong way round which I believe caused the reverse polarity. WP advised that we get an electrician into check the system out as the fuse (circuit breaker) kept blowing on the shower, even now we can only use the shower for less than 3 minutes before it trips out. The electrician fitted a RCD device which means I can just switch it back on before it trips again. The electrician spent most of the day baffling me with science and carring out tests with is big yellow box thingy which gave a reading of 363.

He gave the reason for changing the consumer unit as the old one was dated as it relied on changing fuse wires and was prone to catching fire...ekk! He felt that the old consumer board and become a tangled mess and that somewhere along the line someone as wired into the system to provide power to the garage and used connectors used by Western Power and not installed a separate earthing rod into the garage.

No mention has been made of any bonding conductors to the main gas and water services. Sadly I do not know what all your abbreviations stand for:-

1. TT
2. MET
3. Ze
4. Zs

Also I have been given no paperwork.

Thanks in advance for your help...

 

[Plonker 3]

Sounds like he was trying to scare you into getting your distribution board changed.

When ever I talk to customers I try and keep it as simple as possible without using too much technical information. If the customer starts looking confused then I will give them a print out of some information that I may have on my computer to explain what I was trying to say.

Did he mention anything about earth rods or suppiers earth?

May be worth getting another spark in, post you location and there will be someone on here who could come round and look at it for you?

 

[Engineer54]

Here you go ....

1. TT =Earthing system by means of earth rod(s)
2. MET =Main earthing terminal
3. Ze =Earth loop impedance external (with all earthing conductors at MET disconnected)
4. Zs =Earth loop impedance internal (with all earthing conductors connected)

 

[Engineer54]

Photo's would clear-up a lot of the unknowns for us to advise you futher, on how to proceed on getting your installation back to a safe and operational level etc!!...

 

[Paul.M]

I'd be careful E54 about asking a self confessed "not good at DIY" (as the op as stated) to take off the cu panel to take a pic. I'm not having a go E54, I'm just saying that we need to draw a line somewhere and I believe we are now crossing it.

 

[Des 56]

Have a nose around the areas where both the gas and water services enter the dwelling and look for a fairly large green/yellow cable attached to a clamp on that service,note whether the services supplied enter the dwelling by means of plastic or metal pipes as well

See if a green/yellow cable exits the dwelling and is connected to what is showing of an earth spike in the ground

Look at the incoming supply and see if there is a sticker with PME written on it, also observe if there is a green/yellow entering the enclosure where the supply fuse is located

You may or may not be well advised about a change of consumer unit,these may give better protection for the occupier than the older fuse boards (which are still available for electrical installations) but a new consumer unit does not fix problems,it can in some circumstances highlight a fault that may not blow a fuse,but such things as your value of Ze at the supply is irrelevent to the decision to renew your new consumer unit or not

You would be well advised to enquire into the value of whatever person you have doing the tests to ensure they can back their attendance with related skills ,qualifications etc
This is true of all works carried out,but probably more so with the electrical industry as it stands, with so many pretend sparks roaming free,thats not to imply lack of competence in your present spark,but a generalisation only