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QUESTION:I have seen a 7 kW electric boiler at Plumb Center @ 410. It is ideal
in size for what I need and I may consider using it. Will normal
cooker cable do to wire this up? I will use one 30 amp fuse at the
consumer unit just for the boiler. Can anyone tell me the regs on the
isolation switch, and the wiring of a large current electric
appliance? What earthing will I need, any ideas?
ANSWER: Will 6kw (20,472 Btus) Do?
To make a cheap electric boiler get
1. one 2 foot length of 2 1/4" BSP mild steel pipe (available off the shelf
at some dealers).
2. two 2 1/4" x 1" BSP mild steel tees.
3. two 3 kW 11" long electric immersion heaters (approx 9 at Screwfix)
4. two 2 1/4" saddle clips.
5. two clamp-on pipe thermostats.
6. two 1" BSP x 28mm copper unions.
7. two suitable electrical contactors to take a 3kW supply.
8. Pipe insulation.
a. Screw the tees onto each end of the pipe and have the tees facing
upwards. These are the flow and return.
b. Screw into the pipe ends the electric immersion heaters.
screw the unions into the 1" side of the tees and take off 28mm copper pipe
c. On the flow clamp on the two pipe stats.
d. Clips to wall
e. Wrap in foil and over that with insulation
Have the built-in immersion stats on max (these act as high limits).
Have one contactor operate one immersion heater.
have one pipe stat energise one contactor.
Set one pipe stat to 80C and one to 70-75C as this will act as a step. You
want to put in a simple electric timer from Maplin to prevent cycling and to
bring in each immersion at different times to avoid surge.
If you want a higher output then do the same again and join the flows and
returns of each pipe and the tee off in 28mm copper for a combined flow and
return. This gives then over 40,000 Btus (12 kW).
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