Add up the wattage of everything that will run at the same time, divide by 1,000 to get kVA, and choose a transformer with spare capacity. Then check no single 16A outlet carries more than about 1,760W (16A x 110V). Small tools suit 1.0 to 1.5kVA; a few tools plus lighting suit 3.3kVA; a floor's worth of tools and lights from a three-phase supply suits 10kVA.
Our transformer range
EW code
Rating
Input
Outlets
105842
1.0kVA
230V (13A plug)
1 x 16A
105845
1.5kVA
230V (13A plug)
2 x 16A
105847
3.3kVA
230V (13A plug)
2 x 16A
123254
10kVA
400V 3-phase
4 x 16A, 2 x 32A
Worked example
Six 50m LED festoon kits draw 6 x 130W = 780W. Add, say, a 1,100W drill and the total is about 1.9kW, or 1.9kVA. That points to a 3.3kVA transformer, with the load split over both outlets.
Watch out for
Starting current on motors such as saws and mixers, which can be several times the running load.
Long cable runs, where voltage drop adds up.
The rating plate: check the transformer's continuous rating, not just the headline kVA.
Not sure? Send us the list of what's running and we'll size it for you, usually within the hour.
How many festoon lights can I run off one transformer?
Each of our 50m LED festoon kits draws about 130W (20 heads of 6.5W). A 16A outlet at 110V supplies up to about 1,760W, so add up the kits on each outlet, leave headroom, and keep the total within the transformer's continuous rating. Check the festoon spec sheet for how many kits can be linked in one run, or ask us and we'll work it out for your site.
What is 110V CTE?
110V CTE (centre tapped to earth) is the reduced low voltage supply used on UK construction sites. The site transformer's 110V output is centre-tapped to earth, so each live conductor is only 55V from earth (63.5V on a three-phase supply), and a shock is far less dangerous than from 230V mains.
Need it tomorrow? Order by 1pm.
Send us your list, a drawing or just a description of the job. We'll come back with a quote within an hour and have it on its way next day, or ready to collect from Bristol or London.
