3 phase motor

Duncan Bennett · Jun 21, 2012

Can someone help me with this?

I almost exclusively deal in domestic work, but I've been asked - by a mate - to install a car lift in his garage.

It's a three phase, 400v 6.4amp motor which outputs 2.2kW. I'm running from the Distribution board in swa to the control switch.

My question is, what size of 3 phase Circuit Breaker should i install at the board? Can I get away with 6amp breaker? Also, what's the story with B, C & D curves?

Thanks

Duncan Bennett · Jun 21, 2012

telectrix said:
duncan, you need to know the current capacity of that 1.5mm cable feeding the motor. assuming it's around 16A, then your MCB needs to be rated less than 16A. bearing in mind that the MCB protects the cable. you would need to use a type C to handle the start up current without tripping, so a 10A would seem appropriate. another point to note, if you are not au fait with 3 phase, is that if the motor runs the wrong way you have your phase rotation incorrect and would then neede to swap any 2 phases at the motor isolator.

Cheers Telectrix. I was aware re turning the phases, thanks - gleaned that from today's research

10 amp was my own first thought, but Darkwood suggests 20amp and I think I see where he's coming from in the info he posted in #30.

Darkwood also asked for a pic of the plate and I did take one, just about to get it off my phone and post it here.

Thanks again.

Duncan Bennett · Jun 21, 2012

These are pictures of the plate and of the flexible cable feeding the motor. The other end goes to the isolator and the feed side is wired from SWA. Not great pictures, but I'm pretty sure the stranded flexible cable is 1.5mm. The neutral (unused) is the core seen wrapped around the bottom.

Knobhead · Jun 21, 2012

That’s a high current for a 2.2KW 400V motor. At .85 power factor and 90% efficiency I get 4A. Change to 230V it works out as 7A?
As it’s 2[SUP]nd[/SUP] hand it’s obviously worked before. You’ll just have to try it out. It’s the only thing you can do.

Duncan Bennett · Jun 21, 2012

It was the fact that it had been used before and that it was even pre-wired that nudged me towards agreeing to connect it for him.

Also, he knows the guy in the garage it came from, and has seen it working on several occasions.

I'll definitely let you know how I get on.

Silly Sausage · Jun 21, 2012

Duncan Bennett said:
It was the fact that it had been used before and that it was even pre-wired that nudged me towards agreeing to connect it for him.

Also, he knows the guy in the garage it came from, and has seen it working on several occasions.

I'll definitely let you know how I get on.

Doesn't mean that it's right.
Assumption being one of the 'Mothers of All ???? Ups'

Leave this to Tony!

Knobhead · Jun 21, 2012

If you’ve got a clamp meter let us know what current it does actually take.

Duncan Bennett · Jun 21, 2012

Archy Styrigg said:
Doesn't mean that it's right.
Assumption being one of the 'Mothers of All ???? Ups'

Leave this to Tony!

Agreed, Archy. Hence the reason I came on here for a bit of advice.

Silly Sausage · Jun 21, 2012

Sorry, got distracted by the earlier madness!

Moses · Jun 21, 2012

Tony said:
6.4A is wrong for a 2.2KW 400V motor. It’s for a delta connected 230V motor, for 400V you will have to connect it in star.

Tony I'm no expert on motors.

But you are right the 6.4A rating for a 2.2KW 3P motor is for a delta connected 230V supply.

For Star connected, 400v 3P 2.2KW motor the current will be 3.19A.

So a 6A c-type breaker will suffice with 1.5mm cable.

Darkwood · Jun 21, 2012

Duncan note on your second pic.... SY cable has been utilised to supply motor... but i see the screen has been taped off, make sure you earth the screen as its a possibility if the cable is damage it may become live otherwise, and Note! on my mcb choice, alot of people question why i have picked mcb's alot higher than expected, i cross reference them to manu' guides of mcb's and recommended mcb in relation to motor size.... having said that a 2.2Kw would normally need a 16amp(b) or a 10amp(c); In your case the motor current FLC (full load current) is that of a 3Kw motor hence i have thus given the mcb rating for a 3Kw motor. Following this advice you will eliminate periodic nuisance trips due to inrush.

Duncan Bennett · Jun 21, 2012

No problem, Archy.

I'm actually quite pleased with the way this has gone; i know i don't know much about three phase, but I feel vindicated when I see how interesting this thread has actually become and, if a guy like Tony can be slightly taken aback by the spec. of the motor, then how baffled was I going to be - justification enough for having made the post in the first place :0)

Lilley · Jun 21, 2012

i would use a C10 triple pole. C type to reduce tripping on start up

Darkwood · Jun 21, 2012

Moses said:
Tony I'm no expert on motors.

But you are right the 6.4A rating for a 2.2KW 3P motor is for a delta connected 230V supply.

For Star connected, 400v 3P 2.2KW motor the current will be 3.19A.

So a 6A c-type breaker will suffice with 1.5mm cable.

Check out my posts regarding mcb sizing for this motor, you'll be supprised and hes already shown plate in pic as 6.4amps.

Knobhead · Jun 21, 2012

Moses said:
Tony I'm no expert on motors.

But you are right the 6.4A rating for a 2.2KW 3P motor is for a delta connected 230V supply.

For Star connected, 400v 3P 2.2KW motor the current will be 3.19A.

So a 6A c-type breaker will suffice with 1.5mm cable.

You have to take power factor and efficiency in to account as well.

Darkwood · Jun 21, 2012

Quick question duncan... is the 1.5mm SY the supply from the mains or is it the cable linking motor up to control box?

3 phase motor

Duncan Bennett

-

Duncan Bennett

-

Duncan Bennett

-

Knobhead

Duncan Bennett

-

Silly Sausage

Knobhead

Duncan Bennett

-

Silly Sausage

Moses

Darkwood

Duncan Bennett

-

Lilley

Darkwood

Knobhead

Darkwood

News and Offers from Sponsors

Similar threads

OFFICIAL SPONSORS

YOUR Unread Posts