Current transformer metering producing implausible readings

[Petej999]

Review the attached.

There is no guarantee that the switch operates and isolates correctly, therefore you must check before working on anything

ccan't open it

 

[Julie.]

ccan't open it

Oops

It's the best practice guide 2 from electrical safety first.

Best Practice Guides | Electrical Safety First

Electrical Safety First produces, in association with other industry bodies, a range of Best Practice Guides which provide definitive information and guidance on a range of technical subjects.

www.electricalsafetyfirst.org.uk

Could no-one else open it? Works for me

 

[pc1966]

Oops

It's the best practice guide 2 from electrical safety first.

Best Practice Guides | Electrical Safety First

Electrical Safety First produces, in association with other industry bodies, a range of Best Practice Guides which provide definitive information and guidance on a range of technical subjects.

www.electricalsafetyfirst.org.uk

Could no-one else open it? Works for me

Works OK for me as well.

Using Firefox on desktop so maybe not so good on mobile/tablet?

 

[BrianHJR]

Review the attached.

There is no guarantee that the switch operates and isolates correctly, therefore you must check before working on anyth

Provided there is nothing else to the right of your fused-switch then the CT location is correct, even if putting them on the busbars a bit off. However as already pointed you the meter has to be set with the correct ratio so you get charged for 1A * 230V and not 5A * 230V if the ratio is out by 5, etc.

I’d certainly not trust the meter installers to have got it right. Neither of our NICEIC people thought very much of the install when they visited.

The CT for the main supply looks odd, two of them seem to be on the incoming supply taps but 'blue' L3 is off the busbar as nothing to the left seems to use it.

Yes that strikes odd, they have done it like that because there wasn’t enough space to clamp the grey phase incomer.
And you’re correct, XYZ only run on the brown and black phases.

Final question, how are the metering cables taking out with the cover on? Please tell me they are not crushed under the lid?!!! There is no adequate protective fusing of the voltage tap meter cables so they should be subject to additional protection against mechanical damage / shorting out / etc

The cables go through the front of the chamber and into the back of the meter box through a brass bush fortunately.

Very good point about the metering wires, they should presumably be insulated and sheathed like the rest of the cabling within the chamber?

I’ve attached a couple of photos of the inside of the meter box showing the wires supplying the power for the meters via an MCB - you can hopefully see that they have several cuts on them, fully down to the conductors - as left by the installers.
also a minor point but should the metal backplate in the meter box be bonded?
There‘s currently no proper bonding to the front cover of the bus bar chamber either, other than that tenuously provided by the fixing bolts…

 

[BrianHJR]

So the electrical company were sent back to investigate the metering issues and fitted completely new ones in a different location, rather than bolting the meter box to the front of the bus bar chamber lid they have put it above on the wall.
The install seems to be of a significantly higher standard this time, but there is one potential glaring issue if we ever decide to use the spare switch fuse for anything else in future…



They didn’t leave any instructions for getting the meter readings and I had to work that out myself today.
A much better idea would have been for them to mount the metering box outside on the external wall, so that they wouldn’t have to rely on us for the figures and could send someone out to periodically check it?

The good news is that the meters are now producing plausible readings. The instantaneous import reading for our building showed a KW figure which was completely reasonable for the demand at that point and so we can hopefully now assume that the CTs are set up correctly…

 

[Heriberto Batchellor]

I have encountered a similar problem recently, and I am trying to solve it,by some new devices,i hope these could help me solve my problems