Transformer MCB

[CuteQ]

In my control panel, I have a type B 16Amp MCB for a 240v-110v transformer.

Every time when I started the panel, the MCB always tripped. Not only that, it also tripped the mains’ MCB. (I didn’t design the panel)

Later on I learned that a D type MCB is more suitable for a transformer.

Once the control panel is up and running, it seems to work fine and the MCB doesn’t trip.

So I’m just wondering if I can get away with leaving the MCB I have already got in there or do I have to replace it with a type D?

Thanks

 

[rbulsara]

You already know the answer!

Rafiq Bulsara

http://www.srengineersct.com

 

[ScottyUK]

I would try to use a C curve MCB where possible, rather than a D curve. Most E-I type transformers will be ok on a type C, although toroidal types almost always require a D because of the very high inrush. D curve breakers can be awkward to coordinate with upstream protection unless there is a big size ratio between them.


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If we learn from our mistakes I'm getting a great education!

 

[jraef]

ScottyUK,
I would think that if the Main is occasionally tripping, it would indicate that his inrush may already be exceeding what a C curve will hold at, no?

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[ScottyUK]

jraef,

There are lot of B curve MCBs in the UK - seems to be the default offering by most manufacturers. I tend to use a C curve as default for a circuits feeding sockets, but it's by no means a standard. It's not that hard to trip a 32A type B MCB by plugging in a portable tool transformer or similar.

It would help to know what type of transformer, and what size, was involved, then we wouldn't have to guess!


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If we learn from our mistakes I'm getting a great education!

 

[CuteQ]

Thanks all

3 KvA Transformer 240v-110v, does this help?

 

[ScottyUK]

Yeah, that's pretty big for a 16A breaker. I'd be tempted to protect it with a 20A type C breaker - size the wiring appropriately - and use an MCB on the secondary side for transformer overcurrent protection.


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If we learn from our mistakes I'm getting a great education!