D type MCB - suitable in domestic premises ?

[stunlawless]

Morning everyone,

Just had a quote for a heat pump. MI's say it should be supplied via a 45A D type mcb without RCD.

It's a 230V single phase unit. Pump running current is 19A, start up 32A, with 6kw direct electrical heat top up (not switched on when pump starts), giving 26A extra.

So, maximum demand is 45A continuous, and 32A on start up.

Several things come to mind:

1. 45A supply is marginal
2. Why the need for a Dtype mcb when start current is well below rated current ? surely 32A wouldn't trip a 45A breaker, or is there a huge inrush current for a long time that they're not telling me ?
3. Should I really even contemplate a Dtype breaker in a house ? I thought that these would only be used with welding sets or Xray machines. Haven't done the calcs yet, but I reckon the disconnect time might be a tad long

Also, they specify that it mustn't be connected via an RCD. The place is a farm, no chance of DNO providing an earth, so I'm stuck with TT. I can't see how I can avoid protecting with an RCD under 17th regs.

My impression is that this supplier is used to dealing with industrial suppliers, and hasn't got to grips with domestic installations.

Opinions, facts and comments ?

Thanks, David

Ps probably won't get near the pc much over the weekend, might not see replies until Monday.

 

[Spark123]

I doubt you'll be able to get away without an RCD - especially as it is TT!, the max Zs for a 45 A D type MCB is 0.1 ohms ish which is a push even for a TN system.
Do you really need to use MCBs? Maybe BS88 fuselinks might be a better option?