Using Type C MCB

[ScottishGasMan]

Quick one.

For a heat pump install where the outdoor unit needs a Type-C MCB. Often they use that for heat pump supply alone and separate Type-B 6A MCB to supply the internal controls/valves/pumps etc.

If a CU is limited on space, Would it contravene the regs running the internal components off the Type-C MCB as well? Assuming the correct cable size is used upto a fuse spur supplying the internal components? (Also assuming the equipment manufacturer does not state a preference. And correct RCD type is used for Heat pump)

 

[securespark]

Why a type C?

I would prefer to have the whole system fed from the same point.

Type C require a tighter tolerance on the EFLI: the limit is half that of Type B breakers.

If your max Zs on a Type C conforms, then I can't see a problem.

 

[ScottishGasMan]

Why a type C?

I would prefer to have the whole system fed from the same point.

Type C require a tighter tolerance on the EFLI: the limit is half that of Type B breakers.

If your max Zs on a Type C conforms, then I can't see a problem.

Manufacturer of heat pump (Domestic) states the outdoor unit must be protected by a Type-C MCB due to potential inrush current when starting the compressor.

So Type B-RCB, Type-C MCB, (Generally 3-Slots in the CU gone straight away), if the controls have their own Type-B MCB, and potentially in many cases another MCB for Immersion heater. If they want SPD protection then 2-3 more ways used up.

So quite often they will be looking at needing a Sub-board for new heat pump install.

I'm just wandering if they had 3 spare ways in CU, so they could fit the minimum (Type B RCD, and Type C MCB) if it would be a violation to run some of the indoor equipment off the C-MCB assuming the indoor equipment still has its own fused spur) or whether that would be an acceptable compromise.

This isn't for a particular job, more so just looking at what advice is good and bad for Heating and Electrical installers as to their options/methods they could choose from.

 

[Ragnar_AT]

An MCB needs to protect the cable (overload and short circuit). If the loop impedance is low enough to clear a fault I can’t see any reason not to use a type C for the controls. If required by the manufacturer, use an FCU with appropriate fuse.

 

[ericmark]

A type C has same inrush as a type B twice the size. And there is a problem getting the loop impedance low enough, a socket tester will normally show fault at around 1.9 ohms, so 10 amp type C, or 20 amp type B approx.

Most heat pumps are inverter drive, as otherwise hard to get the loop impedance low enough.

It may be worth looking at a fuse!