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Tim JA
Tim JA, HVAC Technician
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I have a Danfoss DHP-H, recently my consumer unit trip to

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I have a Danfoss DHP-H, recently my consumer unit trip to the HP pump started to trip, not when the compressor starts as you might expect but whilst it is running. I have changed the trip switch twice it still happens. I first thought it might be the soft start but as it does not happen when starting. Any ideas
JA: What's the brand and model of your HVAC unit? How old is it?
Customer: it is a Danfoss DCP-H, it was commissioned in 2012
JA: How long has this been going on? What have you tried so far?
Customer: i6s been happening for a bout 2 weeks, the only thing I have tried is changing the trip in the consumer unit. It can be reset immediately and might run for a couple of hours.
JA: Anything else we should know to help you best?
Customer: The soft start seems to be giving all the right signs. Eg the alarm remains lit to stop you starting it within a minute.
JA: Who makes your lighting?
Customer: Don’t understand the question
JA: The Electrician can help you find the model number for your lighting; I'll connect you shortly. How long has this been going on with your lighting? What have you tried so far?
Customer: im talking about a Heat Source System. ?
Tim JA
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I'm sorry to hear of your DHP-H problem.

Please tell me the type and the rating of the device that's tripping.

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Customer: replied 14 days ago.
AXIOM B32 TRIP SWITCH IN MY CONSUMER UNIT.

Is it an MCB or an RCBO?

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Customer: replied 14 days ago.
Mini cct breaker that only feeds the heat pump system.

OK.  What is the rating of your appliance?

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Customer: replied 14 days ago.
The compressor starting current is 18A but there is a soft start connected. Remember the trip does not occur when the compressor starts. It is intermittent and can trip at any time from 1 hour onwards. To be honest it has not tripped since 1700 yesterday. That is first time it has not tripped overnight.

OK. I wasn't implying anything with my question, but I still need to know the manufacturer's specification for the rating of your appliance.  I believe there are different versions of the DHP-H, so I can't make any assumptions.

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Customer: replied 13 days ago.
The System is a DHP-H-12 Compressor Power 5.7 kw, Start Current per phase soft start 28A

On paper that should be no challenge to a 32A MCB, but they don't last forever, so something worthy of consideration is a failing MCB.

If you know what you're doing with electrics, you could test out this possibility by swapping MCBs with another domestic circuit, like a 32A socket circuit (usually a ring final).

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Customer: replied 13 days ago.
Ok I’ve already done that with a new breaker.

New MCBs can be faulty, but if you're convinced that it's not that then I would verify that the appliance is drawing as little as you think, e.g. with a clamp meter.

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