door heaters

[ollie le roux]

hi there,
i\\\'m installing 4 over door heaters, 65 metres away from the board, drawing 24 amps each, 6000W each. according to the information on your site, a 4mm2 cable would do the job for each of them, this doesn\\\'t take in consideration the voltage drop on such long a run. any suggestions?
Cheers.

[Adam_151]

You will need to use 10mm cable to keep the volt drop below 4%

[Lectrician]

And what is the supply arrangements?? 3 phase I hope?? What other loading is there on site?? You wil have 48amps on atleast one phase with just those heaters!

[theshogun]

4 x24amps =96amps

Thats a lot of load for one phase.

[Damocles]

Some might say that was a problem for the generating company. More immediately it would be a lot of load if you only have a single phase 100A supply at the moment.

__________________
His vorpal blade went snicker-snack

[ban-all-sheds]

ollie le roux wrote:

i\\\'m installing 4 over door heaters, drawing 24 amps each, 6000W each.. any suggestions?

Yes - ask your customer if he's heard of global warming, and ask him WTF he thinks he's doing installing 24kW of over-door heating.

Tell him that he may not have a social conscience, may not give a stuff about the environment, but you do, and you aren't going to do the job.

__________________
I mustn't warn people that the "experts" on the plumbing forum can't be trusted to tell the truth.

[swelec]

googled oven door heaters

nothing came up

what are they ?

( please don't tell me they are heaters for oven doors )

[Lectrician]

Over, to Oven

Warm Air Curtains - Normally in shops.

[mapj1]

Don't forget that the 4% voltage drop is guideline when the maker does not specify otherwise, and supply conditions are unknown, and is certainly correct thinking for socket ciruits where anything may be plugged in.
If however the heaters are rated for example 230v+/-10%, (207V-253V)then a drop greater than 4% would be acceptable, as there is no risk of any other load being applied, and the heaters would be perfectly happy. Most heater type appliences can tolerate a much greater voltage variation than the 4%, particularly those made for the 220V continent originally.
I assume its a big shop, like a multi-level department store, as the leccy bill will be quite high- I presume they know this.

regards M.
PS cable drop calculator on the TLC website.

[ban-all-sheds]

Lectrician wrote:

Warm Air Curtains - Normally in shops.

And a more obscene example of unnecessary energy use, this side of patio heaters, it it hard to imagine.

Our grandchildren will not thank us for this sort of thing.

__________________
I mustn't warn people that the "experts" on the plumbing forum can't be trusted to tell the truth.

[swelec]

swelec wrote:

googled oven door heaters nothing came up what are they ? ( please don't tell me they are heaters for oven doors )

I'm really not a morning person

Air curtains - right I know them

[amtomo999]

Further to reply from mapj1, I agree with your comments, we sometimes get a bit hung up with volt drop.

More important is the safety aspect. The cable should be sized relative to the fuse or MCB rating.

The choice of cable to be such that the resistance (R1+R2) is low enough (combined with the Ze - external earth loop impedance), that in the event of a short circuit or earth fault the fuse will blow (MCB will trip) fast enough to prevent injury.

If an RCD (30mA tripping current) is installed this condition is not really an issue as Max impedance to be less than 50Volts/0.03Amps=1667ohms.

Remember other issues,
-grouping with other cables
-running cables in insulation
-use of rewirable fuses
-method of insulation

Sorry to get a bit techy but safety is important.