Miniature circuit beaker vs fuse in VT secondary wiring

[LSpark]

Is there any reason why I shouldn't use a 3 phase miniature circuit breaker rather than fuses on the secondary (110V) side of a VT?

We've always used red spot fuses in the past but have been offered MCBs in the scheme I'm looking at. I can't think of a good reason not to use the MCBs at the moment but I'm sure there must be a reason we haven't done in the past.

 

[scottf]

It's common to see MCB's used on VT secondaries and I see no reason not too, assuming the performance is acceptable.

 

[LSpark]

Thanks Scott, the only problem I can think of is that it would be harder to lock off as a point of isolation. It's good to know it's common elsewhere.

 

[ptcabb]

I find MCBs preferable, it gives you an indication on when you've lost your VT connection. Useful for undervoltage/frequency functions, absolutely vital for impedance protection.

I rarely encounter fuses anymore, only when retrofitting some older installations. Although I understand there are fuses with indication contacts as well. Never seen them though.

 

[LSpark]

These VTs are for tariff metering and I enable the voltage imbalance alarm on the meter so we get an almost immediate alarm if a phase goes down. MCBs would make fault finding easier.

I like the idea of not having to scrabble around the bottom of my toolbag to find a spare fuse!

 

[purplepete]

We have MCB's on the VT's of our latest switchgear and don't anticipate any problems. They are very handy as there are many MCBs in each compartment and fuse wedges can be easily interchanged mixing up the ratings. If there is an upstream LV fuse locked away in a compartment, make sure the grading is right so on a short-circuit the MCB trips before the fuse.

 

[ScottyUK]

It costs very little to add an auxiliary contact to the MCB and connect it into the 'protection abnormal' alarm or whatever term you use to describe a non-fatal but undesirable state of the protection scheme. A fuse of the size you find on VT secondaries doesn't really have that option.

 

[mgtrp]

Grasshopper fuses will provide an alarm when they blow, and are the right size/scale for protection and control systems. Although I do agree, MCB's are preferable.