4 Pole Contactor

[gtownspark]

I need to wire up 7 water heaters in an office building and the client wants the water heaters to switch off at 5pm when the office closes and switch back on at 7am just before the office opens in the morning.... Can I use a electromechanical timeswitch to operate 2 x 4 pole contactors mounted in a din rail enclosure under the fuseboard? I wasn't sure if it was normal practice to use a 4 pole contactor for 3 or 4 separate single phase circuits instead of 1 3phase circuit? Thanks in advance.

 

[tazz]

Should work fine, use a din rail timer to switch both contactors, and keep in all neat a tidy in 1 housing.

 

[Darkwood]

Your going to load the mains up with 7 storage heaters all at once...have you accounted for this as diversity can be used here if powering in unison - will they be balanced over the phases to minimise load issues?

Is it cost effective to let the water go cold overnight to fully reheat in the morning or are they well insulated and just require the occasional top-up throughout the night?

Caution when selecting contactors here... some brands and models have the 4th pole with a reduced switching/loading capacity as its often acts as a control pole for retaining or simple N/O control signal - majority are rated fully across all poles.

 

[Marvo]

I wouldn't go with 4-pole contactors, stick with 3-pole rather. You only normally use 4-pole if you're switching the neutral.

 

[gtownspark]

Thanks guys, I didn't realise the 4th pole was for a neutral or reduced load...All the cable calcs were done by an engineering design company but on our schedule of circuits it just asks us to control the water heaters with a time switch controlled contactor, as they've requested them all to come on at the same time I can only presume they've taken this into account when applying diversity or not as the case maybe. So I need 2x 4 pole and a 1 pole contactor all switched by 1 time clock in a 10module din rail enclosure.

 

[davesparks]

Or just get a 4 pole with a fully rated 4th pole.
What size contactors are you looking at? I've yet to come across a small one with a lower rated 4th pole.

 

[gtownspark]

Well each water heater is protected by a 16A MCB

 

[Knobhead]

Three pole and a neutral link makes sense to me. If it's four pole it must be early make late break for the neutral.