8.5kw shower install

[ECES20]

Got called out to a shower tripping which has been recently installed by another spark.

8.5kw shower newly installed on existing 6mm2LSF cable not longer than 10m from single phase DB. Protected by a 40A RCBO Type B

(shower current Calculated at 36.95A @ 230v)

when clamped shower was pulling over 56A with load on at load side.
Shower would run for 10 minutes then trip. I believe this is overload given the reading from the clamp meter.
RCBO would fail to reset instantly with shower load off/ pull cord in the off position

I fitted a 50A mcb for curiosity to clamp the circuit again. Clamp at the db was reading 45A, clamp on load side of shower was fluctuating between 76-81A, the circuit held for over 20 minutea before I switched it off.
Can anyone Shed light on why these reading would be so diverse.

 

[Strima]

So you have a 8.5Kw shower pulling 56 amps and you decide to change the OCPD to a higher rated one?

I would say there's a fault with the shower unit rather than the supply. It should still be under warranty.

Has this unit been tripping from installation or has the fault developed?

What is the water pressure like in the property?

 

[ruston]

What is the incoming measured voltage?

 

[Strima]

What is the incoming measured voltage?

I knew there was another question I was going to ask.. ?

 

[ECES20]

it’s a newly fitted shower from triton, possibly 2-3 weeks old.
Has developed a tripping issue.

water pressure is normal, shower unit Isn’t loosing pressure,
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I knew there was another question I was going to ask.. ?

Incoming voltage to shower was reading 231v

 

[Strima]

My moneys on a knackered shower unit.
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Edit: have you check the isolator, if fitted, for loose terminations?

 

[ECES20]

My moneys on a knackered shower unit.

It’s not uncommon to get a faulty out of the box shower unit, hoping this isn’t the cause.
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My moneys on a knackered shower unit.
[automerge]1577996443[/automerge]
Edit: have you check the isolator, if fitted, for loose terminations?

I didn’t check load side connections for tightness but all connections at DB are sound

 

[ruston]

Did it stay at that while the shower was on?
Have you done any inspection of the security of the connections to the terminals to the shower, and the board?
@Strima beat me to that bit.

 

[Wilko]

What is the incoming measured voltage?

Good question !
The shower should be running about 35A and it’s drawing about 55A - either voltage is phase to phase or shower is faulty (?).

 

[ruston]

It’s not uncommon to get a faulty out of the box shower unit, hoping this isn’t the cause.
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I didn’t check load side connections for tightness but all connections at DB are sound

Sorry its taking ages for my pc to post tonight .

 

[Vortigern]

If the clamp meter is not defective then one can only assume there is a lower voltage on the switch supply side indicating a defective switch. Fitted an 8.5 kw shower a couple of months ago got called back as shower was not working. They said it kept going off and if the switched off at the shower switch and back on again then it worked. They said the light was on at the shower. Investigation showed that voltage at the shower was intermittent from 9v A.C. to 100v A.C. Which may account for your varying amp readings. The supply cables at the shower switch were fairly carbonised and there was intermittent connection through the switch on the neutral. New switch remake connections all good.
EDIT: P.S. oops just seen your latest post where you did check connections.

 

[ECES20]

Did it stay at that while the shower was on?
Have you done any inspection of the security of the connections to the terminals to the shower, and the board?
@Strima beat me to that bit.

Connections to shower circuit protective device were all secure and sound. I’ll check all connections tomorrow from pull cord to shower to verify they’re tight.
I can’t imagine a loose connection would cause more current to flow, as in the original post the load side was reading between 76A - 81A where as the DB was reading 45A?

 

[ruston]

Yes , was trying to eliminate from A to B.
As at @Vortigern above.

 

[ECES20]

If the clamp meter is not defective then one can only assume there is a lower voltage on the switch supply side indicating a defective switch. Fitted an 8.5 kw shower a couple of months ago got called back as shower was not working. They said it kept going off and if the switched off at the shower switch and back on again then it worked. They said the light was on at the shower. Investigation showed that voltage at the shower was intermittent from 9v A.C. to 100v A.C. Which may account for your varying amp readings. The supply cables at the shower switch were fairly carbonised and there was intermittent connection through the switch on the neutral. New switch remake connections all good.

Thanks !

Shower switch/pull cord where also fitted as new when shower was installed, I will further inspect pull cord also to determine if it’s faulty
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Good question !
The shower should be running about 35A and it’s drawing about 55A - either voltage is phase to phase or shower is faulty (?).

Single phase supply to DB

It’s pointing towards a faulty shower unit from new, unfortunately for the customer.

 

[davesparks]

as in the original post the load side was reading between 76A - 81A where as the DB was reading 45A?

The load side of what? Which conductor did you clamp around, and what type of clamp meter are you using?
How much time had elapsed between these measurements?

The only reason I can think of for the change in current is that a fault is causing the current to increase in the time it took you to move the clamp meter between the two measurements being taken.

Did you check the resistance and IR of the heating elements when cold and hot?

 

[HappyHippyDad]

Thanks !

Shower switch/pull cord where also fitted as new when shower was installed, I will further inspect pull cord also to determine if it’s faulty
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Single phase supply to DB

It’s pointing towards a faulty shower unit from new, unfortunately for the customer.

Did you go back today ECES? If so what was the outcome? Just interested