3 phase motor

[Duncan Bennett]

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]

For someone that claims to have been in the industry since 1979, and hasn't a clue about MCB curves, let alone simple motor protection beggars believe!!
I'm sure during all those years you came into contact with multi phase motors, domestic (plenty of 3 phase domestic installations) or otherwise.

As for not knowing anything about the differences between B / C / D MCB's, I'm just not going to comment.

Don't you think if I had come across them on a regular basis that I wouldn't be on here asking PERFECTLY legitimate questions about them. And who are you to comment on what I have or haven't done in my career? I'm actually getting some HELP with this question from other board members, so please do try not to keep belittling me - don't you have massively technical work to attend to?

 

[ian.settle1]

Oh dear what?

Basic questions a qualified electrician should know.

 

[ian.settle1]

Yes, it has a three phase distribution board - it's a factory unit. And yes, I realise it's notifiable. And thanks very much for taking the trouble to answer, my knowledge of three phase is written on my thumbnail.

No it isn't it's not domestic.

 

[Duncan Bennett]

Basic questions a qualified electrician should know.

Yeah, thanks, Ian.

 

[mickys86]

As much as I agree that you really should know the difference between a b and a c type breaker there isn't much point throwing comments at the op.

To the original question, tony is our resident motor specialist. I'm sure if you meet him halfway in trying to find the difference between star and delta wiring ( again something you really should know) he will help you massively.

 

[Amp David]

Have a gander at this OP. Will tell you what you need to know regard OCPD size and also whether your VD complies as well as disconnection times

http://www.electriciansforums.net/e...al-regulations/47059-cable-calc-template.html

 

[Knobhead]

There is also this for yoiu to look at http://www.electriciansforums.net/commercial-industrial-electrical/43777-motors.html

 

[mickys86]

See what a nice helpful bunch of People we all are...... Haha

 

[Amp David]

There is also this for yoiu to look at http://www.electriciansforums.net/commercial-industrial-electrical/43777-motors.html

And after reading the full thread a couple of times I reckon you'll know exactly what you will need. A very informative thread is that one.

 

[Darkwood]

As tony already mentioned your motor plate sounds strange... A 2.2kw would usually be around the 4.8amp, the 6.4 you state is normally akin to a 3kw motor but its possible its none standard.
Going by your 6.4FLC rating then you require a 20A mcb and a type B or C will suffice, as you'll realise its far from the 6amp you suggest, and also you did state the ampage as 6.4 so why suggest a lower rated mcb...(6amp); would you put a 10amp mcb on a 13amp heater??.. if you get my drift , its this that has had people question your background.

 

[Duncan Bennett]

Hi Mickys86. Thanks for your answer.

Tony did ask a question on the motor and I replied with the information I have.

Honestly. I'm really surprised by some of the reactions on here; questioning my validity as an electrician? I resat my grade card two months ago - the SJIB must be nuts to have given it to me I think.

Here's my story though - for what it's worth. I served my time with an old lad who had a shop in the Morningside area of Edinburgh. We did rewires, domestic alterations, churches, shop-fitting, that sort of thing. I can tear a domestic house apart and put it back together again without a mark. I also learned a good deal about plumbing, joinery, tiling, painting and decorating, etc. I was a DOMESTIC Electrician - that was my game. I eventually took over from my boss and ran the business myself. I know my limitations though; I wouldn't take on industrial work - I subbed that to guys who could do it. I know sparks who work in factories and look after the machinery there - they know their stuff - I wouldn't have a clue, so I don't take on that kind of work.

I then left the trade altogether in a career change which took me into professional football - on the admin. side, I know my limitations in that respect as well. After a number of years - first with the Club, and then as a freelance photographer - I decided to return to the trade last year. Things have changed a bit, but I worked through the books, sat the exam at Select, and had my gradecard renewed by the SJIB.

I'm now picking up where I left off - I don't take on industrial work and I DON'T work with motors, and if that's a hanging offence then I'm sorry. I change sockets, and switches for Mrs. Blogs, I put up light fittings for Mrs. Tuppence-worth. I'm working on an estimate to wire a new build home, and another to revamp a bathroom.

I cam on here because a mate asked me to wire his electric ramp: It came from another garage. Whoever took it apart also supplied it with the control switches, isolator and swa cable still intact. Basically, all I have to do is fix the cable to the surfaces and reattach the SWA gland at the board. But I thought I'd just come on here and check on the breaker. I didn't mean to instigate a war: check my membership details; i never swear, make snide comments or belittle users. I also apportion 'thanks' on as many occasions as I can.

I really admire guys like Tony who are experts in their field, and I have loads of respect for all the guys who swap mathematical formulas on here - they obviously work hard at knowing their game. I'm a domestic electrician, pure and simple - I have no allusions of being more than that. But things have changed a lot since I was last on the tools - I'm getting to grips with it but, honestly, I have neither the need nor the will to start learning about three phase electric motors. The job I'm doing is a one-off for a young mate who's just starting out, I have no intention of adding that sort of work to my jobbing CV

These boards are fantastic though. Most of the time I just come on to glean information. I don't pretend to know it all and these boards have probably saved me hundreds of research hours. Occasionally (as you can see) I also ask a question. But to be berated and belittled for doing so! Why? If you think it's a stupid question then isn't it easier just NOT to say anything. Is there anyone on these boards who doesn't have some aspect of their trade which they're not sure off? My boss used to big me up 'cause I had a deft touch and could 'fish' a cable out of a lathe and plaster ceiling from 15 yards in record time. Have ALL the sparks on here done that? Not that that makes me clever, but it was one of the things I was good at as a domestic spark. On the other hand, I didn't come across many three phase motors in my line of work. Delta and Star!! Last time I looked at that was in college - about 40 years ago.

Anyway, if no one minds too much then I'll continue to use these boards for research, and I might even make a post or two, but I'll make sure I'm qualified enough to know the answer first.

And thanks, again, Micky for your help.

 

[Darkwood]

check my post 25 you may have missed it while writing all that, these are manufactered mcb guidelines for a 6.4amp motor.

 

[Duncan Bennett]

check my post 25 you may have missed it while writing all that, these are manufactered mcb guidelines for a 6.4amp motor.

Exactly what I was looking for, Darkwood. Many thanks, and yes, it was a bit stupid to suggest a 6 amp, I don't even know why I did. But I'd spent two and a half hours trying to find the answer myself before putting the question on the board, and my head was spinning with it. :-(

Thanks again, much appreciated

 

[telectrix]

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.

 

[Darkwood]

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.

Tel .... the motor and its flex will be protected by an overload device and wont see much more than the overload setting for the motor, the supply to the ramp would at a guess without questioning the install details be a 2.5mm swa covered by a 20(b) mcb..... this will be what is required unless the cable calcs are asking for larger ccc due to install methods.
Duncan...
I suspect the ramp has inverter control hence the strange ampage for motor (delta set up), you should refer to ramp instructions for mcb rating but if not available my suggestion should suffice, be nice if you could post a pic of motor plate or give details of ramp manufacturer.