Heater start up currents

[buttonmoon]

Hi fellas

I've got an outdoor heating circuit that I'm trying to fault find.

There are four heaters under a parasol each rated at 1.5kW that are tripping two MCBs in series. One is on the main board the other is in a separate unit dedicated to the outdoor circuit. When the heaters are cold if all four heaters are plugged in then both Mcbs trip instantly. If only two are plugged in it starts and then you can plug the other two in and there's no problem. Then when it times out if it's switched back on immediately then they come on without a problem.

Both MCBs are B types BSEN 60898 hager and MK.
There is no problem with IR
The measured resistance of a heater when cold is 4 ohms
This would give each one a starting current of 57.5 A
So the four together would have a startup current of 230 A or 52 kW

My first thought was to change the MCBs to C or D types but on reflection of these figures that would just result in a tripped main switch. I am thinking of some sort of soft start current control option but I haven't used one before and I'm not sure if that's the best solution.

Apparently it used to work, but I don't see how.

All thoughts welcome.

 

[buttonmoon]

No they don't have 13 A plugs, they have small connectors about 20mm wide with 2 rounded pins and a flat earth strip along one edge. I don't know what they're called and they have no internal fuses.

 

[Knobhead]

No they don't have 13 A plugs, they have small connectors about 20mm wide with 2 rounded pins and a flat earth strip along one edge. I don't know what they're called and they have no internal fuses.

For gods sake I'm running out of Blood Pressure pills ! ! ! !

 

[Octopus]

No they don't have 13 A plugs, they have small connectors about 20mm wide with 2 rounded pins and a flat earth strip along one edge. I don't know what they're called and they have no internal fuses.

Sorry mate but do you think you should be doing this work?

 

[buttonmoon]

Apology accepted, but out of the 10,000 or so appliances I've PAT tested I've never come across a connector that's exactly like this. So it's rare but my god boys PM me your addresses and I'll send you some pills seems like you need them .

 

[Knobhead]

What apology?

Murdoch, did you apologise? Because I know I didn't.

You're comment about PAT testing confirms my thoughts, you're not an electrician.

 

[SYKRAPS]

Looking forward to the conclusion to this one........................

 

[ShropshireLad]

plug type

Are these "euro" or "shuko" type plugs?

 

[tlangdon12]

Schuko seems to fit the OP's description. They are rated to 16A. Hope the OP can get a full description of what tripped when the MCBs were changed.

 

[buttonmoon]

Soft start installed, works fine, still no problems 2 months later. Sorry about the delay.