20amp FCU or higher?

[bobsyeruncle]

Ive got an american style tumble dryer that must be hard wired. The instructions state minimum 2.5mm cable from a 30 amp supply.

It is 4.5KW, can i have it from the 32 amp MCB that i have spare to a 20 amp Fused Switch? I can find any 30 - 32amp fused switch units so the next one up is a 45amp cooker switch!

 

[AndyPRK]

20 or 45a switches are not fused.

 

[bobsyeruncle]

so lets change the question slightly, 32amp mcb to under counter Connection Unit with a 20A accessible switch?

 

[Echo the husky]

The 32A fuse at the consumer unit is the fuse, a 45-50A cooker switch will be fine as a local isolator, though the last one I installed I used a 32A MEM Excel switch disconnector with a gland in the bottom for the dryers 4mm² flex. If the manufacturers state a 30A supply is required, connecting it to a 20A switch fuse isn't a good idea. The fuse running at almost 20A will run hot and cause damage.

Installing a new final circuit is also notifiable work

 

[Echo the husky]

so lets change the question slightly, 32amp mcb to under counter Connection Unit with a 20A accessible switch?

You cannot use a 20A switch, it will soon burn out with a 4.5KW load.

Why are you so against using properly rated equipment?

 

[sparkwright]

A 4.5 kW load works out to be just under 20 amp, so one does have to wonder why a 20 amp should burn out.

If you wanted to play safe, you could use a 30-50 amp switch.

In a way it seems odd requesting a 30 amp supply for a just under 20 amp appliance.

In theory it would make sense to use a 20 amp MCB with a 20 amp minimum switch. Though as stated, it could get hot and burn out. The manufactures do state a 30 amp fuse, so that must be taken into account. Please correct me here.

However, it seems you need to use a minimum flex of 2.5 mm2. This is probably too large to fit into the flex outlet hole provided on most 20 amp switches.

With that in mind, I'd be inclined to use a cooker switch, rated between 30-50 amp, with a fixed cable running from here to a 30-50 amp cooker outlet, where you can then connect the 2.5 mm2 appliance flex.

Or, to save all that work, fit a PVC surface pattress at the switch, and fit a plastic CTS gland in the bottom so the flex can be secured here.

 

[sparkwright]

Presumably the op would be expected to run 4.0 mm2 cable from the consumer unit..

 

[bobsyeruncle]

I initially thought that i would need 4mm cable but the manufacturers instructions do say 2.5mm.

 

[sparkwright]

Do they mean 2.5 mm2 flex just beween the switch and the appliance though?

EDIT. Misquoted cable size given.

 

[bobsyeruncle]

Extract from instructions

This dryer is supplied without an electric
cord and plug. It must be connected by a
competent electrician to a single-phase
electricity supply at the voltage shown on
the dataplate, using a suitable fixed wiring
installation in accordance with local and
national wiring regulations. A 3-wire
circular cord of minimum conductor size
2.5mm cross-section area should be
used. A 30A supply fuse should be used,
and a switch with a minimum contact
separation of 3mm in both poles must be
incorporated into the fixed wiring for dryer
disconnection. This disconnection switch
should be accessible to the user after
installation.

 

[sparkwright]

The 2.5 mm2 minimum round cable is referring to the flex between the appliance and the isolator switch only.

I would use 4 or even 6 mm2 cable flat T+E from the consumer unit to the isolator switch.

 

[endecotp]

The "2.5mm" in the instructions you've quoted is referring to the flex between the dryer and the wall.
The "fixed wiring", i.e. from the wall to the CU, should be "in accordance with ... regulations", which I think probably means 4mm^2.

 

[bobsyeruncle]

Ok, sounds good to me, Thanks folks 6mm it is

 

[sparkwright]

The "2.5mm" in the instructions you've quoted is referring to the flex between the dryer and the wall.
The "fixed wiring", i.e. from the wall to the CU, should be "in accordance with ... regulations", which I think probably means 4mm^2.

I'm inclined to agree. See my edit on a previous post where I misquoted their cable size.

 

[sparkwright]

6 mm2 is more readily available to buy, and for the difference in price may prove future-proof should you need to add something.