Fixed 110v installation

[robsparx]

I have been wiring up a workshop for a customer, and went back the other day and he had bought 4 16A 110v sockets, and a fixed 3kva transformer

He wants me to wire these 4 off 1 transformer. So I have wired the transformer into the board, to go on a 16A supply.

At the 110v side am i right in saying the cable i use would have to be able to take about 28A? (3kva at 240v=13A, 3kva at 110v= 27A) I thought it would have to, but portable trannys have leads with 1.5mm cable so i'm not so sure

Never come across 110v fixed installations before so i'm just a bit confused about this

 

[UNG]

I would install a CU/DB on the secondary side of the transformer as you would with a 240v supply to feed the 110v sockets

 

[Hawk81]

as above fit a db on the 110v side. Make sure and use double pole mcbs.

 

[robsparx]

yes having thought about it that sounds like the best way. a 16a circuit for each socket (or maybe 2 on 1 16A)

 

[robsparx]

What about the cable sizes?

And i guess the cu would have to be adapted, 2 55v into the main switch, then 2 out to feed each 2pole mcb?

 

[UNG]

Check that the transformer secondary has a centre tap and this MUST be connected to earth if no centre tap then this transformer is unsuitable for workshop use as fault voltage will be above 55v

 

[UNG]

What about the cable sizes?

And i guess the cu would have to be adapted, 2 55v into the main switch, then 2 out to feed each 2pole mcb?

If you have 2 x 55v secondary windings these should be connected in series and joint between the windings connected to earth the other ends of the windings will go to the main switch on you DB

The earth tap will only allow a voltage of 55v to earth under fault conditions

 

[robsparx]

I'm sounding like a right spanner here, but have 0 experience with 110v. How do i check it has a centre tap? the 110v side has an earth connection

 

[UNG]

If the secondary is a single winding for the 110v there will / should be three terminals one will be labelled centre or CTE the other two will indcate voltage as 0v and 110v alternatively it will indicate 55v between centre connection and each of the other two connections

 

[robsparx]

the transformer has 55v - CTE - 55v

Ah i guess CTE stands for Centre Tapped Earth?

 

[UNG]

The terminals labelled 55v go to the main switch on the 110v DB CTE is connected to earth all sorted

 

[robsparx]

I'm just trying to over complicate things again.

And i take it i use 2 brown wires instead of brown and blue, as each carries 55v?

 

[davelerave]

ya 2 phase colours and earth for the 110v sockets(for 55-0-55)

if the trafo needs overload protection sometimes it can be fitted at the 110v board.

rcd as well if required(dunno what the rules are in the uk for reduced low-voltage)