Calculating the correct circuit breaker

[Dev]

I have electric gates and one (or maybe both, I dunno) of the motors is shorting.

The gates are on their own trip at the consumer board but when they short it trips the main breaker. This displeases SWMBO.



Connected to that circuit are 2 230v 2a50hz motors with max power of 450W and a brain and intercom that run off a 13a PSU delivering them 12DC

The current breaker is a 32a type B

To me, if the dedicated trip is not going before the main one then its not working right. So my question is, how do I determine what it SHOULD be?

 

[wheresmejumper]

is it tripping the rcd,bypassing the 32A?

 

[rich r]

Is the 32A breaker just a MCB or is it an RCBO (ie an MCB with a built in RCD)?

I would tend to agree that it may well be an earth fault, and as such it's the RCD that's tripping rather than the overcurrent protection. Using RCBOs instead of MCBs might limit what it trips. Obviously the right thing to do would be to fix the fault on the motor(s).

 

[Dev]

The motors are under the gate posts and a helpful neighbour knocked one of the lids slightly when digging out the driveway during the last heavy snow. As a result it slowly filled with water, shorting the motor.
Lucky enough the power tripped when we at home so it was easy enough to flick back but if that had happened while we were at work, or on holiday, then that could have caused problems. I thought the whole point of it being on a separate breaker was so that didn't happen in the event of a fault!

Heres a picture of the trip that on the gate supply (the one that isn't being tripped)

 

[piman]

Hello Dev,

your supposition is correct and technically known as discrimination. I would not have thought that a breaker greater than 6A is required for your gate and certainly not a 32A breaker.

Alec

 

[wheresmejumper]

that is an mcb,and wont trip if it is an earth leakage fault,which is highly likely if water has gotten into the system.

 

[the snooper]

looking at what you posted I would imagine the lot to be a 1000 watts or just under which works out around 4.2 amps so your 32 amp breaker is a fire hazard

 

[piman]

Hello WMJ,

an MCB will trip with an earth fault as the current is likely to be much greater than the breaker rating assuming good earthing.
An RCD or RCBO is not the only device that trips with an earth fault, they are just more sensitive.

Alec

 

[Dev]

Ah ha, so definitely a croc'o's**t then. So does everyone agree that a 6A breaker is what's needed?

Now anyone who's seen my thread about wiring a VFD inverter knows I'm not a spark but in this case it looks pretty much plug in - I can isolate the consumer board and replace the breaker on the bus board which should be within my abilities.

What do I need to purchase, a 6A RCD, RCDO or MCB?


Pretty poor show by the installer tbh. But it's been working fine for the past 3 years and was only rendered unserviceable by a JCB in fairness

 

[the snooper]

was only rendered unserviceable by a JCB in fairness

no the jcb only showed up the installers bad workmanship

 

[Dev]

True enough. If you're ever looking gates doing I can recommend who not to use.

 

[wheresmejumper]

Hello WMJ,

an MCB will trip with an earth fault as the current is likely to be much greater than the breaker rating assuming good earthing.
An RCD or RCBO is not the only device that trips with an earth fault, they are just more sensitive.

Alec

Hi Alec

I think you are right,but in my experience leakage between N and E will always trip the RCD.impedance effects which trip technically,but i think a fault between L and E is more prone to trip an mcb

its been a while since i held a pliers though

 

[brightspark]

normaly gates are fed of a 2,5mm cable with a 16amp mcb back at source and are also fitted with an rcd and an mcb in the controll box