MAJOR electrical issues in 5 year old house - any ideas?

[Jeremy Harris]

IIRC, the 3 phase models were late to shift to inverter control.  This makes sense, as an inverter controlled unit has a three (sometimes more) phase motor.  They rectify the incoming AC to DC, then drive the multi-phase motor with the inverter drive, which is really a variable frequency AC drive.  For a 3 phase inverter controlled unit, the 3 phase would be rectified to DC, then used to drive the motor variable frequency inverter.   From the symptoms described, with a shorted motor phase, it sounds like direct AC drive to me.  One "feature" of variable frequency drives is that they rarely, if ever, damage the motor; the electronics in the drive unit tends shut down a hell of a lot faster than a motor under fault conditions, and will usually just instantly fail. 

 

I've built a lot of variable frequency motor drives, for things like my electric motorcycle, electric bikes and an electric boat and have yet to damage a motor (and all my motors are three phase machines in essence).  I've blown a fair few motor controllers, though, until the current generation, where there is so much protection built in that the controller just shuts down within a µs or two if a problem develops (or if I do lunatic things on the motorcycle - hard not to when you have 100% torque at zero rpm...).

[jack]

I got hold of the model number. According to the data sheet it's inverter driven (note: I may have been misremembered the comment about the short circuit being on one coil):

 

[Onoff]

If the vfd goes t!ts up can't it become a regenerative load itself? RCD won't protect against the resultant overvoltage.

[Onoff]

Here you go, had to go to the States to find this:

 

https://www.callmendel.com/blog/can-your-air-conditioner-cause-a-power-surge-how-to-protect-your-home/

[Onoff]

Appendix 16 of the latest regs,  p507 onwards goes into detail about SPDs in some detail with lots of diagrams depending on the earth arrangement.

[jack]

Thanks for that.

 

I think they're about to become effectively compulsory in many installations, so my electrician had already been reading up on them.

 

Suspect this job brought forward his study a bit!

[Onoff]

22 minutes ago, jack said:

Thanks for that.

 

I think they're about to become effectively compulsory in many installations, so my electrician had already been reading up on them.

 

Suspect this job brought forward his study a bit!

 

Maybe worth delving into the section on lightning protection zones too? 

 

Nick, with his eidetic memory will be able to reel off the relevant sub sections shortly!

[jack]

10 minutes ago, Onoff said:

Maybe worth delving into the section on lightning protection zones too? 

 

Yep, he's been through all that - that's the type 1, type 2 etc stuff, right?

[Onoff]

13 minutes ago, jack said:

 

Yep, he's been through all that - that's the type 1, type 2 etc stuff, right?

 

Circular diagram, left hand page...not got it in front of me!