Mains sockets keep tripping

[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?

 

[bigalw35]

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

The reason is that to check an mcb it would have to generate a fault current of whatever the mcb being tested, which generally could be up to 63amps, but with an rcd/rcbo the fault current would only need to be 30/100/500 Ma, at the worst 1/2 amp, big difference

 

[Adamwallace]

The reason is that to check an mcb it would have to generate a fault current of whatever the mcb being tested, which generally could be up to 63amps, but with an rcd/rcbo the fault current would only need to be 30/100/500 Ma, at the worst 1/2 amp, big difference

Wow. Bit above my head but great for all that so many thanks. Cheers

 

[RandallC]

For info:
MCB can be checked by current injection to confirm correct operation. Have spent many happy hours with a secondary current injection test set on IDMT, CMM, VAJ, etc etc protection relays for Industrial supplies. The kit could be used for domestic MCBs BUT the cost would be prohibitive, cheaper just to replace the MCB.

Whilst on the subject:
ELCB (earth leakage circuit breaker) (bear with the description) senses the difference between what goes out on the Live and returns on the Neutral wires. ANY difference is assumed to be some loss (leakage) of the live to earth. These days most ELCBs are 30mA.

ELCBs will NOT protect you from being electrocuted if you touch Live and Neutral They should protect against fatal shock if you touch Live and Earth.

An MCB is the modern equivalent of a Fuse. MCBs like Fuses require time to operate. That time is dependant on the current passed through them. The larger the current over the rated current of the MCB/Fuse the faster it trips.
BUT
They come in different ratings (like fuses) some trip quickly and some don't.

So ELCBs trip if there is a leakage of the live to Earth.

MCBs trip if there is an overcurrent (overload, excessive current in greater than the MCB rating)

All kit ages and hence needs testing or replacing if suspect and replacement costs significantly outweigh testing.

Happy to discuss

 

[Adamwallace]

A

For info:
MCB can be checked by current injection to confirm correct operation. Have spent many happy hours with a secondary current injection test set on IDMT, CMM, VAJ, etc etc protection relays for Industrial supplies. The kit could be used for domestic MCBs BUT the cost would be prohibitive, cheaper just to replace the MCB.

Whilst on the subject:
ELCB (earth leakage circuit breaker) (bear with the description) senses the difference between what goes out on the Live and returns on the Neutral wires. ANY difference is assumed to be some loss (leakage) of the live to earth. These days most ELCBs are 30mA.

ELCBs will NOT protect you from being electrocuted if you touch Live and Neutral They should protect against fatal shock if you touch Live and Earth.

An MCB is the modern equivalent of a Fuse. MCBs like Fuses require time to operate. That time is dependant on the current passed through them. The larger the current over the rated current of the MCB/Fuse the faster it trips.
BUT
They come in different ratings (like fuses) some trip quickly and some don't.

So ELCBs trip if there is a leakage of the live to Earth.

MCBs trip if there is an overcurrent (overload, excessive current in greater than the MCB rating)

All kit ages and hence needs testing or replacing if suspect and replacement costs significantly outweigh testing.

Happy to discuss

All makes sense thanks. Have now ordered replacement MCB. Will see what happens. Many thanks.

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[autorouter]

I'd always imagined they work on the same principle.

MCBs trip if the current is more than the specified trip current. It has a thermal and a magnetic trip. If it's a large overcurrent, the magnetic force it generates will activate a mechanical trip. If it's a small overcurrent, the heat buildup in the thermal trip will activate the mechanical trip.

An RCD monitors the difference between the outgoing and returning currents. If the difference is more than a tiny amount (typically 30 milliamps) the mechanical trip will activate. A person touching a live conductor will cause some current to flow through the body to earth. An RCD detects this. 30mA is a tolerable current for an average healthy human.

 

[Adamwallace]

MCBs trip if the current is more than the specified trip current. It has a thermal and a magnetic trip. If it's a large overcurrent, the magnetic force it generates will activate a mechanical trip. If it's a small overcurrent, the heat buildup in the thermal trip will activate the mechanical trip.

An RCD monitors the difference between the outgoing and returning currents. If the difference is more than a tiny amount (typically 30 milliamps) the mechanical trip will activate. A person touching a live conductor will cause some current to flow through the body to earth. An RCD detects this. 30mA is a tolerable current for an average healthy human.

That is completely understandable. Many thanks

 

[Adamwallace]

MCBs trip if the current is more than the specified trip current. It has a thermal and a magnetic trip. If it's a large overcurrent, the magnetic force it generates will activate a mechanical trip. If it's a small overcurrent, the heat buildup in the thermal trip will activate the mechanical trip.

An RCD monitors the difference between the outgoing and returning currents. If the difference is more than a tiny amount (typically 30 milliamps) the mechanical trip will activate. A person touching a live conductor will cause some current to flow through the body to earth. An RCD detects this. 30mA is a tolerable current for an average healthy human.

This might be a dumb question, but would there be any point putting a surge protector on the hook-up line?

 

[autorouter]

This might be a dumb question, but would there be any point putting a surge protector on the hook-up line?

There's two kinds of surge protector. One type protects against short spikes induced by for example lightning or a big motor nearby. The other type is a voltage stabiliser that protects against a sustained surge or sag in voltage, maybe for several minutes.

The spike protector is cheap and is more popular in areas where electric storms are common, like the Alps. Voltage stabilisers are usually unnecessary in most of Europe, but in the remoter parts, or in Morocco for example, it's a wise precaution. In the UK they are not really necessary.

 

[Adamwallace]

That's great. Many thanks