Mains sockets keep tripping (1 Viewer)

[Adamwallace]

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?

 

[Adamwallace]

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

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.

 

[icantremember]

No picture right now. However, only the mains SOCKETS stop working. Fridge, space & water heaters still work.

Just a thought, do you have an inverter wired into the system?

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[Adamwallace]

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...

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

 

[Adamwallace]

Just a thought, do you have an inverter wired into the system?

Nope

 

[Adamwallace]

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

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.

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[Adamwallace]

I am not sure which MCB is tripping. Is it the one in the van or the one at the post?

If it is the one in the van then it is not the cable causing it.

Van. Thanks

 

[Adamwallace]

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...

Good type face, if a little shouty

 

[Eggs]

I don't understand why a techie couldn't diagnose a faulty MCB.

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[Adamwallace]

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.

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.

 

[Adamwallace]

I don't understand why a techie couldn't diagnose a faulty MCB.

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!!

 

[dabhand]

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

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[Adamwallace]

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

Gee that's interesting. I'll have a look at that as well as replacing the mcb.

 

[pappajohn]

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.

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.

 

[Gromett]

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.

Van. Thanks

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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[dabhand]

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.

Or a dead short caused by something like a leak

 

[Gromett]

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.

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

 

[Adamwallace]

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.

Thanks mate. Seems about right. I'm going for mcb for now.

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[Hirsch]

Hmmm. What gadget?

Sorry , I was in a hurry. I was referring to the socket tester. A starting point for me too.

 

[Adamwallace]

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

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!

 

[Adamwallace]

Sorry , I was in a hurry. I was referring to the socket tester. A starting point for me too.

Lovely. Thanks

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[autorouter]

Do you have a picture of the 16A breaker? Does it have a 'Test' button on it, as well as the trip switch toggle?

Are we quite sure this breaker is an MCB not an RCBO? An RCBO has a 'Test' button, an MCB doesn't.

 

[Adamwallace]

Are we quite sure this breaker is an MCB not an RCBO? An RCBO has a 'Test' button, an MCB doesn't.

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?

 

[pappajohn]

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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[Eggs]

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.

I'm no sparky but I thought a RCD protects all the circuits, whereas a RCBO protects only 1 circuit.

 

[Adamwallace]

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.

So is there some advantage?

 

[Gromett]

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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[pappajohn]

I'm no sparky but I thought a RCD protects all the circuits, whereas a RCBO protects only 1 circuit.

An RCD doesn't protect overload... An RCBO does.

 

[Adamwallace]

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.

I'm 99.9 % certain I have an MCB. My unit is 2018 reg.

 

[bigalw35]

I don't understand why a techie couldn't diagnose a faulty MCB.

There are no meters/test equipment that can check MCB,s, RCD,s yes but not mcb’s

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[Adamwallace]

There are no meters/test equipment that can check MCB,s, RCD,s yes but not mcb’s

How interesting. I wonder why that is. I'd always imagined they work on the same principle.