Dodgy advice

[matt1e]

Ever noticed how much incorrect information there is on the net?
A couple of the engineers at our place asked me for info on motors, star/delta motor control etc and since I've Got the day off today I thought I would print up some useful info for them, anyway here is one pic I came across.

This of course is not the way to do it, for those who don't have much experience with motors consider it homework as to why not

Matt

 

[conny]

To change direction of a motor without a reverse switch simply change any two phase supply leads at the motor terminal block.

 

[ban-all-sheds]

Wouldn't you want the phase change to apply to the entire thing, not just part of the wiring?

Wouldn't changing it where shown make the motor go one way during start up and then go pear shaped when it came time for the starter to drop out?

Disclaimer - I know SFA about 3-phase motor control.

 

[matt1e]

Wouldn't you want the phase change to apply to the entire thing, not just part of the wiring?

Wouldn't changing it where shown make the motor go one way during start up and then go pear shaped when it came time for the starter to drop out?

Disclaimer - I know SFA about 3-phase motor control.

you know more than the person who did that drawing BAS
yes,no matter which two phases are swapped where shown, the motor will single phase when it switches from star to delta

Matt

 

[matt1e]

To change direction of a motor without a reverse switch simply change any two phase supply leads at the motor terminal block.

As above but note that in the case of a star/delta wired motor you have to swap both supply pairs (as there are two of each phase)
some would swap over at the supply fuses as its easier

Matt

 

[bhm1712]

Or you can change the 2 phases over at the supply terminals on the L1, L2 and L3 rail. However this is not good practice as if correct coloured cables have been used for 3 phase, it messes the colour scheme up and can lead to problems for a future engineer!

 

[Bolty]

Swapping L1 and L2 is one way to change direction but i prefer the swapping over of 2 sets of windings.

I find in some MCC's it's easier to get to the outgoing terminals to the motor then playing around with connections after the isolator or fuses.

Swapping over U1 and V1 and U2 and V2 will change the direction.

Simples.

Bolty.

 

[bhm1712]

thats the general rule at our place...Changing over the 2 sets of windings.

 

[pjcomp]

In answer to the original question, that has always been the problem with the internet, no editorial control. Those of us who remember its early days (early '90s for instance) saw all this developing, but these days it's treated as the fount of all knowledge with no critical checking of whether that knowledge is any good.

I can cite another example, though unfortunately I've lost the link - forum supposedly giving electrical advice, and one of the resident experts describing "safe zones" as the areas where it's safe to drill, not where it's safe to put cables.

pj

 

[ban-all-sheds]

I don't know which is scarier.

The he would drill there, or would install cables anywhere but there.