NSH repair

[SUNRAY]

My tenant reported the NSH not heating, there is only one and not yet a year old.
My initial tests during the day, so no cheap rate, found the circuit between CU (E7 tail) and NSH terminals, via 20A DP switch, tested OK using the pictured meter on Ω range.

Next thing I needed was power so added a wire link to CU to bypass E7 contactor and expected to see a 3.3KW load... nothing.

The 20A switch prooved to be HR... more MK junk.
Replaced and straightaway meter beeped rapidly indicating overload on 40A range when power applied... Instant reaction?... Ooops. On 400A range I saw 82.8A

However half a second of thought later...

 

[securespark]

Can't think where the problem lies.

 

[SUNRAY]

Can't think where the problem lies.

Actually the problem is I thought I'd put up a second edit of the picture.
In the meantime I repeat there is only one 3.3KW load on the E7 switched supply.

Initially I'd only clipped the meter on one turn but then used the meter at the heater.

 

[securespark]

Can I literally see the bigger picture?

 

[Nozzle]

Measuring multiple times the current as there are multiple passes of wire through the meter

Nozzle

 

[SUNRAY]

Can I literally see the bigger picture?

That's it:

I linked from the 24hr bussbar to the E7 tail with a random piece of wire, the first bit I picked up happened to be a coiled length of green/yellow 2.5mm² tri-rated.

 

[securespark]

Ah, gotcha.

Wasn't sure about the G/Y at first!

Is it anything to do with the coil?

 

[SUNRAY]

Ah, gotcha.

Wasn't sure about the G/Y at first!

Is it anything to do with the coil?

Well yes as I was measuring the current several times, as Nozzle correctly identifies too.
As mentioned, initially tried to measure the current on a single turn and finding zero used the meter for tests at the heater. After replacing the switch I casually 'parked' the meter on the coil on the 40A range. My initial WTF reaction was to its rapid beeping for overload, something I'd not heard before.

 

[securespark]

Sorry, I completely missed Nozzle's post

 

[SUNRAY]

Sorry, I completely missed Nozzle's post

My usual trick is to start writing a reply, have lunch, make some phone calls, pick the kids up from school/college, have dinner, watch some TV then complete my answer and post... That's when I find three others have also made similar replies

 

[securespark]

Sounds familiar!

 

[SUNRAY]

For completeness the whole CU, until a year ago there were 3 NSH on the right hand RCD, now there's just the one with the 2 circuits repurposed onto 24H on the 2 centre RCBO's shown switched off.