Mains sockets keep tripping

A

Adamwallace

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Oct 28, 2020
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Location
Dereham, UK
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77,305
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Adam wallace murray
Exp
C class since 2006
When hooking up to mains supply on site in UK my consumer unit 16 amp trip switch (mcb? - I can never recall the right name) for the mains power sockets trips as soon as I switch on the main RCD.

This happens even without anything plugged in. All the other mains circuits remain ok (eg space & water heaters, fridge). I'm on a seasonal pitch and no probs for the first week or two, then tripped maybe once a week for another 3 weeks, and now is immediate if I flick on the trip switch.

All was ok on a previous site and I've had the 'van electrics professionally checked (found a loose connection, sorted, tested fine, but problem continued on return to present site. I have tried hooking up to different power pillars and changed pitch completely at one point. Other people on neighbouring pitches are not having problems. I'm now thinking of touring other sites to see if problem limited to this site.

On the other hand, I had a similar problem at home some years ago, which was solved by changing the relevant trip switch.
Any thought or suggestions?
 
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andy63 said:
in the ops original post it states all the other circuits remain on and working... so the rcd can't have tripped... it says the 16 amp breaker protecting the sockets circuit trips immediately... that would indicate a short circuit ..
Andy
Click to expand...
Exactly. Rcd NOT tripped. Short circuit IS indicated but £200 of techie testing says no short circuit. Seems to point to faulty MCB, similar to domestic situation described in my op.
 
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RandallC said:
Re last post ANDY 63 (in case beating post)

No if the RCD trips all should be dead if not you have a problem that needs Pro help.

Opps how did i get this type face...
Click to expand...
Thanks for that. Pro help already engaged at cost of £200. Says if any future probs, it must be site supply issue. Pursued that, but issue there is that we're the only van affected. Again, now pointing to faulty mcb
 
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andy63 said:
in the ops original post it states all the other circuits remain on and working... so the rcd can't have tripped... it says the 16 amp breaker protecting the sockets circuit trips immediately... that would indicate a short circuit ..
Andy
Click to expand...
I think I've answered this already but said answer seems to have disappeared. Exactly right but techie tells me no short circuit. Suggests faulty mcb I think.
 
Upvote 0
I don't understand why a techie couldn't diagnose a faulty MCB.
 
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Raul said:
Well if your circuits test ok with the tester, is only two things left:
The feed plug and cable,
And the mcb that trips could be faulty.
Click to expand...
There are so many replies I'm losing track, so apologies if this duplicates an earlier response. I agree, & think it must be the mcb. I'm now ordering a new one.

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Eggs said:
I don't understand why a techie couldn't diagnose a faulty MCB.
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Me neither. Slight loss of faith in his answers. BUT had similar problem some years ago with domestic supply and it wad only the third 'leccie who identified the root cause. Others suggested we change all our white goods!!
 
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I had a similar fault a couple of years ago, it turned out to be two things, a faulty blue plug on the mains lead and a leaking water pipe on the hot water side dripping onto the main power supply which is underneath the boiler in the boot. Changed the hot water pipe in the boot and the blue plug, then all ok. Fused a few aires in France first though (y)
 
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dabhand said:
I had a similar fault a couple of years ago, it turned out to be two things, a faulty blue plug on the mains lead and a leaking water pipe on the hot water side dripping onto the main power supply which is underneath the boiler in the boot. Changed the hot water pipe in the boot and the blue plug, then all ok. Fused a few aires in France first though (y)
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Gee that's interesting. I'll have a look at that as well as replacing the mcb.
 
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Adamwallace said:
All the other mains circuits remain ok (eg space & water heaters, fridge). I'm on a seasonal pitch and no probs for the first week or two, then tripped maybe once a week for another 3 weeks, and now is immediate if I flick on the trip switch.
Click to expand...
Certainly illiminates the wiring.
If it was a wiring fault it would trip from day one....not once a week for 3 weeks after being on hookup for a couple of weeks with no problem.
 
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MCBs do age. They will start tripping at lower initial surges until they fail completely and won't reset.

IF you have ruled out everything connected to the panel including as Jim suggested the charger, then a failing MCB is likely the cause.


Adamwallace said:
Van. Thanks
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Won't be the cable then. If it was the cable, it would trip the RCD in the post.
An MCB only deals with high current like a fuse. It doesn't deal with earth faults for example.

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Gromett said:
MCBs do age. They will start tripping at lower initial surges until they fail completely and won't reset.

IF you have ruled out everything connected to the panel including as Jim suggested the charger, then a failing MCB is likely the cause.



Won't be the cable then. If it was the cable, it would trip the RCD in the post.
An MCB only deals with high current like a fuse. It doesn't deal with earth faults for example.
Click to expand...
Or a dead short caused by something like a leak (y)
 
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I just searched for a comprehensive explanation of how an MCB works to show the ageing failure mode.

This is the mechanism that causes the trip on over current.
1622662782970.png


A high current flowing through the coil wrapped around this is what causes it to trip under abnormal operation (fault/short circuit).
As they age, the spring can lose it's potency and allow a much lower current to be able to exceed the springs capacity to resist. It will eventually get to the point where even a 1Amp current can overcome the spring.

See the section Principle of short circuit protection of miniature circuit breaker.

What is a miniature circuit breaker? - Quisure

Miniature circuit breaker(MCB) is a small-capacity plastic case circuit breaker with very compact structure. It is a branch of low-voltage circuit...
www.quisure.com www.quisure.com
 
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Gromett said:
I just searched for a comprehensive explanation of how an MCB works to show the ageing failure mode.

This is the mechanism that causes the trip on over current.
View attachment 503047

A high current flowing through the coil wrapped around this is what causes it to trip under abnormal operation (fault/short circuit).
As they age, the spring can lose it's potency and allow a much lower current to be able to exceed the springs capacity to resist. It will eventually get to the point where even a 1Amp current can overcome the spring.

See the section Principle of short circuit protection of miniature circuit breaker.

What is a miniature circuit breaker? - Quisure

Miniature circuit breaker(MCB) is a small-capacity plastic case circuit breaker with very compact structure. It is a branch of low-voltage circuit...
www.quisure.com www.quisure.com
Click to expand...
Now THAT explains a lot! When my old 'leccie said mcb's can "develop a memory", it sounded a bit woo-woo, but what you've said makes absolute logical sense. Thank you so much!👍

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autorouter said:
Are we quite sure this breaker is an MCB not an RCBO? An RCBO has a 'Test' button, an MCB doesn't.
Click to expand...
I'm not in the van at present, so don't know for sure, but I am fairly sure it's an mcb. Apart from the reset button, what difference does it make?
 
Upvote 0
An RCBO will trip with an earth fault same as an RCD and an overload fault the same as an MCB.
They are considerably more expensive than an RCD or an MCB.
£70 to £80 for some makes.
 
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pappajohn said:
An RCBO will trip with an earth fault same as an RCD and an overload fault the same as an MCB.
They are considerably more expensive than an RCD or an MCB.
£70 to £80 for some makes.
Click to expand...
I'm no sparky but I thought a RCD protects all the circuits, whereas a RCBO protects only 1 circuit.

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Upvote 0
pappajohn said:
An RCBO will trip with an earth fault same as an RCD and an overload fault the same as an MCB.
They are considerably more expensive than an RCD or an MCB.
£70 to £80 for some makes.
Click to expand...
So is there some advantage?
 
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In most "modern" motorhomes you will find an RCD supplying a couple of MCBs.

I can't imagine any manufacturer putting RCBOs in a motorhome. But I am happy to be proven wrong on that one.
 
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Gromett said:
In most "modern" motorhomes you will find an RCD supplying a couple of MCBs.

I can't imagine any manufacturer putting RCBOs in a motorhome. But I am happy to be proven wrong on that one.
Click to expand...
I'm 99.9 % certain I have an MCB. My unit is 2018 reg.
 
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