Wye Delta without 1M

[Gustav]

Hello,

an old colleague told me a few weeks ago, that if I am using a wye delta starter without the 1M contactor, that I do have to observe the voltage for the remaining two contactors.
He said that I need to look for contactors able to switch 480V mulitplied by sqroot of three = 832V.

No I wanted to explain this to the supplier of the contactor, but I am unable to explain it.

Can anyone explain me this or was it just a joke?

Thanks
Best regards
Gustav

 

[brian john]

Standard wye delta closed transition starter? Without a 1M? Obviously not a standard wye delta?

What are the existing starters?

 

[Gustav]

Why standard?

It is no old one existing - new application - customers asks for cost reduction and usiong the version without 1M

 

[jim dungar]

Hello,

an old colleague told me a few weeks ago, that if I am using a wye delta starter without the 1M contactor, that I do have to observe the voltage for the remaining two contactors.
He said that I need to look for contactors able to switch 480V mulitplied by sqroot of three = 832V.

No I wanted to explain this to the supplier of the contactor, but I am unable to explain it.

Can anyone explain me this or was it just a joke?

Thanks
Best regards
Gustav

You must have some information confused.

If you do not have the 1M contactor then you are starting the motor at full line voltage using the delta windings. Yes, the delta windings are 1.732x the wye voltage but you can never exceed the line-line voltage.

 

[Jraef]

Your friend is incorrect about the voltage issue, it makes no difference. You cannot get more voltage out of a circuit than you put into it (unless you use a transformer, and where is the transformer?). Maybe he is thinking that the motor is operating like a rotating transformer, but he is incorrect about the direction the pseudo-transformation is going. Y-Delta starting is just taking advantage of all of the winding ends being brought out to terminals so that you can reconfigure how they are connected. In Y the effective voltage across the windings is reduced by the square-root of 3, but nothing is ever increased anywhere.

Just FYI, this is done all the time in the elevator industry, in fact almost all Y-Delta starters for elevator motors are started without the 1M contactor. The only reason is because it saves them on the cost of one more contactor in the large volume of controllers they supply annually. There is no really valid reason to assume the extra safety risk for a one-off plant site.

The big potential (no pun intended) safety problem with not using the 1M contactor is that 3 of the motor leads are then energized at all times. Look at a Y-Delta power wiring schematic and just imagine that 1M is closed at all times. Power still cannot flow through any of the windings without one of the other two contactors being closed. If your service / maintenance people are unaware of this, it poses a severe risk to them, or more specifically, a risk to people prone to not follow the proper LOTO rules. In other words, sometimes people not trained as professional electricians will ASSume that if the motor starter is Off, the motor leads are dead. In that case, 3 of them are NOT. If you ALWAYS lock out the line side disconnect then this is a non-issue.

The reason they get away with this in the elevator industry is that technically, elevator controls are NOT permitted to be service by people who are not licensed to do so, and those that are will get specific training as to the potential and non-standard risks involved. Most inspectors will NOT accept a 2-contactor Y-Delta starter for any application that is not in a similar circumstance.

 

[jim dungar]

If you do not have the 1M contactor then you are starting the motor at full line voltage using the delta windings. Yes, the delta windings are 1.732x the wye voltage but you can never exceed the line-line voltage.

My bad.

See Jraef's explanation instead.

 

[chris kennedy]

What is a 1M contactor?

 

[Jraef]

What is a 1M contactor?

In the US (JIC) wiring diagram standards, an open transition Y-Delta motor starter typically consists of 3 contactors: 1M, 2M, and S. When starting, 1M and S are closed, putting the motor windings in a Wye (or Star) pattern. Then there is a brief transition period in which S opens, taking the motor off line, and immediately afterwards, 2M closes which reconfigures the windings into a Delta pattern for full voltage (full torque) running.

 

[jim dungar]

In the US (JIC) wiring diagram standards, an open transition Y-Delta motor starter typically consists of 3 contactors: 1M, 2M, and S. When starting, 1M and S are closed, putting the motor windings in a Wye (or Star) pattern. Then there is a brief transition period in which S opens, taking the motor off line, and immediately afterwards, 2M closes which reconfigures the windings into a Delta pattern for full voltage (full torque) running.

When "stopped" the 1M contactor is open disconnecting the motor entirely from the circuit. Because the OP does not have a 1M contactor, one side of each winding is always energized (unless the disconnect switch is opened). This is similar in concept to using a 1-pole float switch to control a 240V 2-pole motor.

 

[Jraef]

When "stopped" the 1M contactor is open disconnecting the motor entirely from the circuit. Because the OP does not have a 1M contactor, one side of each winding is always energized (unless the disconnect switch is opened). This is similar in concept to using a 1-pole float switch to control a 240V 2-pole motor.

Yes, that's why I said (or at least implied) it was not a good practice for every day installations and likely to be rejected by an inspector in anything other than an elevator controller. I don't know that for sure though, maybe some of our inspector members would like to address that last point. The first time I came across this in the Elevator industry I argued against it as a potential violation of the Code, but could not find anything supporting that contention. The Elevator people insisted to me that they had been doing it this way for 50 years without a rejection.

Regardless, I still think it is not a "best practice".

 

[don_resqcapt19]

... Most inspectors will NOT accept a 2-contactor Y-Delta starter for any application that is not in a similar circumstance.

What code section would permit an inspector to reject this? A controller is not required to open all of the conductors of a circuit like a disconnect is. It is only required to open enough conductors to stop the current flow to the equipment. It is not required nor intended to make the equipment safe to work on.

 

[Jraef]

What code section would permit an inspector to reject this? A controller is not required to open all of the conductors of a circuit like a disconnect is. It is only required to open enough conductors to stop the current flow to the equipment. It is not required nor intended to make the equipment safe to work on.

I know, as I said above I could not find support for my own argument. I may very well be wrong about that part of it, but I have seen an AHJ reject the idea on starters from an OEM for a bunch of refrigeration compressors. As we know, you can challenge an AHJ but that isn't a good use of your time and resources just to save on the cost of a contactor.