110v supply issue?

[pc1966]

Why don't building site transformers have MCB's on the fly leads to what they are supplying?

Some do it seems, from the Blakley data sheet:

Overcurrent Protection
Input MCBs are Type “D” and output MCBs are Type “C”, to BS EN 60898.
All 32A sockets are individually protected by 32A DP MCBs.
Lighting circuits without RCD are protected by 10A or 16A DP MCB, as detailed above.

Taken from this product:

Site Power Transformer with MCB Protection | Blakley Electrics

Site Power Transformer with MCB Protection from Blakley Electrics, designers, manufacturers and distributors of high performance Power and Lighting products.

www.blakley.co.uk

Their 4kVA one has a 16A DP input breaker, more in keeping with that sort of rating (unlike the 32A mentioned earlier in this thread).

 

[Ian1981]

Why don't building site transformers have MCB's on the fly leads to what they are supplying?

You have a thermal trip built into the transformer and over current protection and in the 13amp plug top.
larger kva transformer distribution feeding multiple equipment will have over current protection and mcbs on show on the side of the transformer
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Like this type

 

[Mike Johnson]

The two outlet one I bought from Screwfix about five years ago does not have anything like that.

 

[Ian1981]

The two outlet one I bought from Screwfix about five years ago does not have anything like that.

What size is it tho, 1.5kva, 3kva?
They just plug into the supply and have the secondary side protected

 

[davesparks]

Why don't building site transformers have MCB's on the fly leads to what they are supplying?

The outlets on the transformers have the protection.

These are very basic questions for someone claiming to be an electrician

 

[Mike Johnson]

1.5kva only, not running anything fancy, only a vacuum and a biscuit jointer.
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These are very basic questions for someone claiming to be an electrician

It's been eleven years since I retired and anywhere near a building site so have had to make room in my brain for other things.

 

[davesparks]

1.5kva only, not running anything fancy, only a vacuum and a biscuit jointer.
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It's been eleven years since I retired and anywhere near a building site so have had to make room in my brain for other things.

The basic principle of protecting circuits should still be there though surely?

 

[Mike Johnson]

Yes of course it should, and it relies on the thermal re-set, if it has one.

 

[Steve46]

found this drawing today

 

[westward10]

It is showing a 10 way dist board with 16A type C protective devices. It doesn't indicate whether single or double-pole devices but it should be double-pole.

 

[pc1966]

It is showing a 10 way dist board with 16A type C protective devices. It doesn't indicate whether single or double-pole devices but it should be double-pole.

Oddly it is not showing MCB specified at the sockets, unless that is specified off-page or in the list of parts?

Certainly the ideal solution to me would be a board right next to the transformer (less than 3m cable) and all DP MCB there.

 

[Ian1981]

Oddly it is not showing MCB specified at the sockets, unless that is specified off-page or in the list of parts?

Certainly the ideal solution to me would be a board right next to the transformer (less than 3m cable) and all DP MCB there.

You don’t need mcbs at the socket positions if you have DP mcbs at the origin of the circuits

 

[westward10]

The spec is poorly worded indicating single-pole and neutral, it should say two-pole and earth.

 

[pc1966]

You don’t need mcbs at the socket positions if you have DP mcbs at the origin of the circuits

Indeed not, but the OP said the sockets had integrated MCBs which is a cause of confusion here.

 

[Ian1981]

Indeed not, but the OP said the sockets had integrated MCBs which is a cause of confusion here.

You’re correct, missed that , apologies