MCBs

[charliemercieca]

Can anyone please tell me how to check whether an MCB is good or not? ... Thanks for your help

 

[Zeespark]

Continuity test between the in and out terminals, with the MCB switched on.

AndyGuinness

 

[m4tty]

Continuity test between the in and out terminals, with the MCB switched on.AndyGuinness

That'll blow the fuse in your tester if circuit is live make sure it's removed before you do what andy has stated. What is the problem with the mcb?

 

[charliemercieca]

every time I need to switch the mcb off, when I switch it on again it trips 2 or 3 times before it stays on .... thanks

 

[Andy™]

That'll blow the fuse in your tester if circuit is live make sure it's removed before you do what andy has stated. What is the problem with the mcb?

no it wont. itll only risk blowing the fuse in tester if the breaker is switch off and there is a load connected

 

[Sidewinder]

What mcb is it?

Curve and rating please?

What is it suppplying?

P.S. WELCOME to the forum!

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[quote name='Andy

 

[NozSpark]

So does mine,,,,,apparently

Although I'm not quite stupid enough to try it

 

[m4tty]

I thought it would blow the fuse sorry ... Just goes to show I've never done it

 

[Sidewinder]

M4tty,

It depends on your meter, I actually did this 4 times today when live fault finding and testing on a control system swapping between V a.c. & ohms on the 110V a.c. control, 240V a.c. & the 400V 3ph a.c. supplies.

However, I was using a Fluke 87 DMM, which is quite well protected against incorrect inputs.

Not sure about the MFT's etc. or any other meter, but, this one survived fine!

AGAIN!!!

The pressure of a production breakdown sometimes takes over.

 

[ProDave]

every time I need to switch the mcb off, when I switch it on again it trips 2 or 3 times before it stays on .... thanks

What load is connected?

Have you tried measuring the load current with a clamp ammeter?

 

[Andy™]

I thought it would blow the fuse sorry ... Just goes to show I've never done it

if the MCB is closed, there will be no voltage diference between the probes, so it wont even tell you its a live circuit

if the MCB is open, then it could blow a fuse depending on tester & setting

 

[m4tty]

Mine clicks I think when doing a continuity test on live circuit that's a Megger 1552. It certainly makes you take the probes off quick. Only done it once tho but blew a hole in my best cutters yesterday.

 

[Andy™]

Mine clicks I think when doing a continuity test on live circuit that's a Megger 1552.

mine blew a fuse when i IR'd a live circuit a few month back...

 

[Sidewinder]

Don't think I have ever used my MFT on any ohms setting on a live cct, sorry to know.

My DMM now is another matter!!!

 

[charliemercieca]

The MCB is a MEM 16 amps and when tested the load with a clamp meter, the reading was only 9 amps and only lighting, no motors.

 

[Jono Pashley]

Metrel wont let you test is theres voltage present when it shouldnt be. Saved me a few fuses by now i think.

 

[batty]

The MCB is a MEM 16 amps and when tested the load with a clamp meter, the reading was only 9 amps and only lighting, no motors.

9 Amps of lighting that is quite a load what sort of lighting is it? welcome to the forum by the way.

 

[Doc Hudson]

The MCB is a MEM 16 amps and when tested the load with a clamp meter, the reading was only 9 amps and only lighting, no motors.

Welcome to the forum, I am assuming this is some commercial or industrial application. Is there a large bank of lights all coming on together causing inrush current problems. What type of MCB? 'B', 'C', 'D'?

Doc H.

 

[Zeespark]

When I posted My reply, I answered on the pretense that the MCB would be completely removed from the CU and all wiring unterminated

AndyGuinness

 

[Revved Up Sparky]

If practicable I would simply swap the MCB for another one (one that is compatible with the DB and with the same rating of course). This could identify the problem very quickly.