Replace an MCB

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Ellwood

32 posts

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#154079 17-Oct-2014 12:09

Hey Chaps,

Got a circuit that won't reset after cut the power to it, it didn't trip i turned it off. anyway now when i hit the button to turn it back on it pops straight back off, i have a feeling its a stuffed MCB as the little red button to turn it off is pretty much jammed and has no spring back in it.

So my question is can i just knock the power off at the main switch, pull the MCB out, head to the hardware store get a like for like replacement and bang it in?

Or am i gonna need to call a sparky?

The offending MCB is the one on the right:

Cheers..

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#1156761 17-Oct-2014 12:20

Looks like you can do the work yourself if you are the homeowner and occupier
http://www.med.govt.nz/energysafety/consumer/safe-living-with-electricity/electrical-wiring-in-your-home

You'll end up with a replacement like the one on the far right, with a switch rather than button.

Of course, only choose one with the same current rating

wellygary

8335 posts

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#1156763 17-Oct-2014 12:22

From memory they seat into a ceramic fitting ( which is where the wiring terminates) and this is mounted on the board behind,

Just read of the amperage and go and get a replacement one (like the one at the end of the row) and whack it in,

These are a user replacable fitting, ( jsut like re-winding a fuse holder was in the "good old days")

DarthKermit

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#1156767 17-Oct-2014 12:24

Those older types of MCBs with the two buttons are tempermental, it's typical for the user to be unable to reset them.

Whatifthespacekeyhadneverbeeninvented?

gzt

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#1156771 17-Oct-2014 12:25

I am not 100% sure they are all socketed even though many appear to have a socket. How to tell the difference?

dickytim

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#1156774 17-Oct-2014 12:28

don't quote me but they look like plug in MCB's so you should be able to pull it out and plug in the new one.

NZI, ABB etc. all make them, you may not find them at a hardware store but an electrical wholesaler should stock them.

Definitely get the same amperage.

gzt

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#1156775 17-Oct-2014 12:29

nickb800: Looks like you can do the work yourself if you are the homeowner and occupier
http://www.med.govt.nz/energysafety/consumer/safe-living-with-electricity/electrical-wiring-in-your-home

You'll end up with a replacement like the one on the far right, with a switch rather than button.

Of course, only choose one with the same current rating

I would guess you might be right but in that article it is not clear that circuit breakers are in the same category as fuses as user replaceable.

1. The page says nothing about replacing circuit breakers
2. The last item on that page is: after resetting a circuit breaker:

"If the circuit breaker continues to trip, call a licensed electrician.".

dolsen

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#1156795 17-Oct-2014 13:02

Just to confirm, swap it with the one on the left (looks like it just pulls out, can't quite tell from the picture).
While it is out, you can also try whacking it a few times on the side and then retry.

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gregmcc

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#1157120 17-Oct-2014 19:59

Ellwood: Hey Chaps,

Got a circuit that won't reset after cut the power to it, it didn't trip i turned it off. anyway now when i hit the button to turn it back on it pops straight back off, i have a feeling its a stuffed MCB as the little red button to turn it off is pretty much jammed and has no spring back in it.

So my question is can i just knock the power off at the main switch, pull the MCB out, head to the hardware store get a like for like replacement and bang it in?

Or am i gonna need to call a sparky?

The offending MCB is the one on the right:

Cheers..

Quite well know for this type of failure, remove the plug in circuit breaker, give it a light tap on the side with the head of the screw driver, there is a good chance this will fix it.

If is does plug it back in. If it doesn't go buy a new one.

They ARE a plug in unit as demonstrated by the one next to it that has been replaced.

richms

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#1157135 17-Oct-2014 20:12

Replace it, those old 2 button ones are really old now and go super-over-sensitive IME.

Richard rich.ms

Ellwood

32 posts

Geek

#1157290 18-Oct-2014 08:37

Cheers guys, I swapped it with the other one I have off and that works fine on that circuit, plugged the dodgy one back in and same deal. Popped out straight away..

Must admit I hadn't even consider the legal implications of doing it, more whether I was able, but figured its pretty low risk so I'll head to Bunnings today and get a new one, and plan to swap the rest of the button ones out.

Much appreciate your help.

Niel

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#1157342 18-Oct-2014 09:54

This applies to an owner-occupied home, and is what I understand from the wiring code published for consumers: Anything plug-in you can buy in a local retail shop is fine (e.g. Bunnings). You are not allowed to open the switchboard panel and work on the back of it. You are not allowed to change/move permanent wiring or fittings. You are allowed to replace fittings (wall sockets, switches, and lights) with a similar type. You are allowed to replace a fuse wire carrier (not the holder/socket) with a plug-in circuit breaker.

You can never have enough Volvos!

floydie

474 posts

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#1157592 18-Oct-2014 19:55

just make sure you use the correct rating..for lighting circuits you should ONLY be using 10 amp breakers. power circuits are 16 and 20 amp.

Yabanize

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#1157599 18-Oct-2014 20:08

floydie: just make sure you use the correct rating..for lighting circuits you should ONLY be using 10 amp breakers. power circuits are 16 and 20 amp.

Most house sockets are only rated for 10 amps?

nickb800

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#1157603 18-Oct-2014 20:24

Yabanize:
floydie: just make sure you use the correct rating..for lighting circuits you should ONLY be using 10 amp breakers. power circuits are 16 and 20 amp.

Most house sockets are only rated for 10 amps?

But a circuit will have many sockets attached, so a 10amp breaker would break if you used more than one outlet fully. The main function of a circuit breaker is to protect the cable from overload or short circuits

Aredwood

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#1157879 19-Oct-2014 14:14

floydie: just make sure you use the correct rating..for lighting circuits you should ONLY be using 10 amp breakers. power circuits are 16 and 20 amp.

Lots of lighting circuits are only rated for 5 amps. And there are some power circuits that are only rated for 10 amps. It depends on the size of cable used, length of cable (due to voltage drop) and insulation. Newer installs it is assumed the cables will be installed in insulation - So lower current ratings have to be used to stop the cables from overheating. Old installs cables were exposed to air so they could carry more current without overheating.

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