Connecting Supply For Motor

[pga.elec]

Have been asked a question which I am not 100% on, and I have never been asked before.

Motors have 6 studs inside the terminal chamber, U1, V1, W1, and then the internal wiring of the motor and the studs on the opposite side of the chamber read W2, U2, and V2. If the motor is a Star configuration, the links are placed across W2, U2, and V2. If it is a Delta configuration, the links are placed across U1 to W2, V1 to U2 and W1 to V2. The line supply cable is connected L1 to U1 stud, L2 to V1 and L3 to W1, and if the motor needs to be reversed, then two of the line phases are swapped.

I have been asked, that due to the tightness of connections, can the line supply phases be connected to the other side connections, W2, U2, V2, and the links changed to the other side if Star configuration. So L1 would connect to U2, L2 to V2 and L3 to W2.

My first thought would be this cannot be carried out like this, but then again, I have never been asked this question. All line supply cables have always been connected to U1, V1, W1 and the links fitted accordingly. Can anyone confirm please and the reasoning whether it is acceptable or not?

Many thanks in advance.

 

[telectrix]

can't see why not. as each terminal is just the end of a winding.

 

[Lucien Nunes]

Yes, as Tel says it's just the other end of each winding. The relative phasing of the three windings is preserved if the delta links connect the 'finish' i.e. end '2' of each winding to the 'start' i.e. end '1' of the next, and the star links interconnect either all the '1's or '2's with the supply is across all the '2's or all the '1's respectively.

What you must not do (and which can happen when a star-delta starter is incorrectly connected) is reverse one winding relative to the other two, by making arbitrary links that don't follow the sequence.

 

[PEG]

Only minor addition to the debate,is to check that the motor is rated to run in either direction. Some can be reversed electrically,but are not designed,mechanically,to run in both CW and CCW.

It applies mainly to older and larger motors,in regard to threaded drives,accessories,and scrolled seals,etc. Even something as seemingly minor,as pulling cooling air,via the fan,from a *dirty" process side,and not the clean side

 

[Lucien Nunes]

These are good points that do get overlooked. In this case though, I think they want the motor to run in the same direction but with the line connections to the other end of the windings, to ease congestion in the terminal box.

We had some units once where the cooling fan capacitors were failing, resulting in the fans running slowly backwards and filling the equipment space with airborne gunk. Things started overheating properly once the air filters, which looked OK from the outside, became completely choked with dust on the inside.

 

[edexlab]

Slightly off topic
I've been working on a job installed by a Dutch firm this week which had control panels with a fan at the top, I opened the door to check something and saw a lot of dust in a fairly new panel and the fan filter full of dust on the outside

I checked the fan and it was blowing into the panel, which is something I've always thought was wrong, with the fan at the top any heat rising would normally be extracted with cooler air coming in from the bottom of the panel, I queried it and was told it's meant to be blowing in????

Has anyone seen this set up used before

 

[James]

My preference is to have a filtered fan low down blowing in to the panel and an exhaust vent with a course mesh or louvred vent near the top.

Blowing in, can be good because it makes the enclosure slightly pressured and helps to keep dirt out.
If you suck air out and rely on a vent to allow it in, when the vent becomes clogged with dirt, air is sucked in through any gap it can find,
Door seals, mounting holes, conduits etc.