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Topic Title: Make break isolator trip RCD?
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Created On: 09 October 2017 09:54 PM
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 09 October 2017 09:54 PM
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NE1

Posts: 35
Joined: 07 March 2017

I've had a call about a tripping problem with a hot tub that has a rotary isolator on it. Could it be the neutral is in in the early make, late break contact, would it cause the imbalance?
 09 October 2017 11:56 PM
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mapj1

Posts: 9670
Joined: 22 July 2004

it can certainly cause RCD problems. The trick is to reverse the roles of the contacts

-------------------------
regards Mike
 10 October 2017 09:42 AM
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AJJewsbury

Posts: 16083
Joined: 13 August 2003

Although might suggest poor N-PE insulation? Open N with L still connected will only cause an imbalance if the current can find somewhere else to go...
- Andy.
 11 October 2017 09:38 PM
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NE1

Posts: 35
Joined: 07 March 2017

Mapj1 I would have thought it to be worse that way as there is a voltage being taken before the neutral has connected. As Andy said. Have you done this way before?
Just really wondering if anyone has suffered from this being an issue before?
And as Andy said I only know of a problem because of leakage to earth. But because of hot tubs maybe there's something in there.
Thank you both for your replies so far.
 11 October 2017 10:31 PM
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AJJewsbury

Posts: 16083
Joined: 13 August 2003

Mapj1 I would have thought it to be worse that way

I think both Mike and I misread you original post, thinking you were asking if the L/N contacts had been switched around (or weren't deliberately selective, so down to manufacturing tolerances as to which one opens first/closes last) and N was open at some point in time when L was connected.

I suppose it doesn't have to be poor insulation as such - N-PE capacitance - e.g. as part of a filter - will pass more a.c. current when N alone is open and is dragged up to line voltage via the load. In some cases it might be enough to break the camel's back as far as the RCD is concerned.

- Andy.
 12 October 2017 08:15 AM
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Zoomup

Posts: 3422
Joined: 20 February 2014

If the rotary switch is turned ON and then the local hot tube controls are used there should be no R.C.D. tripping if there is not a fault present. Normally the rotary switch is a main switch/isolator. The rotary switch normally (from memory) does not switch on a load. The load current is only present after the local integral switches are used on the tub. Thus both L and N are fully present when the local tub control switches are operated. Most modern tubs have a control panel mounted on them for the user to use when in the tub. The controls work through extra low Voltage or pneumatic controls for safety. Some modern hot tub controls are wireless in operation.

Have you disconnected the tub from the supply and tested the heating elements with an insulation resistance tester? It is best to totally disconnect the heating elements from their supply cables before doing this as hot tubs have vulnerable electronic components. An element may have a low resistance to earth due to dampness entering the end of the heating element, especially if the tub is outdoors.

It is a good idea to look for water leaks at pumps and other electrical connections under the tub. Also ensure that the supply cable has tight terminal connections as well. Excellent earthing is essential.



Z.

Edited: 12 October 2017 at 08:59 AM by Zoomup
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