# in delta wiring through soft start



## John Valdes (May 17, 2007)

What is the question? I don't understand. If you have a 6 or 12 lead motor, delta is the run configuration. Wye is the start configuration.
Since you are asking about a soft start you will use the delta configuration. 
Check the nameplate or inside the connection box for the delta/run wiring diagram.

The soft start will ramp start the motor and this will greatly reduce the starting current. It good on the equipment too.


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## Paulusgnome (Mar 28, 2009)

balpav said:


> how does in delta motor wiring through a soft start effect start up amps? it is a 250hp motor 460v.282fla.


Normal rule for this sort of arrangement is that the current seen by the soft start will be 58% of line current.


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## John Valdes (May 17, 2007)

Paulusgnome said:


> Normal rule for this sort of arrangement is that the current seen by the soft start will be 58% of line current.


How do you get that number?


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## Paulusgnome (Mar 28, 2009)

Its the same as when you wire up a star-delta starter, the overload relay wires inside the delta and sees 1 / sqrt3 times line current, about 0.5773 if you want a bit more precision.

Here, the OP wants to wire the soft starter inside the delta of a delta-connected motor, a valid cost-saving technique provided the usual caveats are observed.


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## John Valdes (May 17, 2007)

Paulusgnome said:


> Its the same as when you wire up a star-delta starter, the overload relay wires inside the delta and sees 1 / sqrt3 times line current, about 0.5773 if you want a bit more precision.
> 
> Here, the OP wants to wire the soft starter inside the delta of a delta-connected motor, a valid cost-saving technique provided the usual caveats are observed.


I still don't get it. I know how a wye/start delta/run configuration works and if you say its "1/sqrt3 times line current" who am I to argue with you.

But I can tell you an electronic soft start is not like the wye/start, delta/run. Nothing like it. "Wire the soft starter inside the delta of the delta connected motor", makes absolutely no sense to me.

A soft start requires nothing but a connected motor and a few parameter settings for ramp and decel. Nothing more.


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## Paulusgnome (Mar 28, 2009)

Not being able to post a circuit diagram makes explaining this a bit harder.

The motor in question will be of the type that you can connect to run with the windings in delta.

It is possible to wire in a soft starter so that each phase leg of the soft start is in series with one motor winding, with the whole motor + starter set wired in delta, and this arrangement will permit soft starting of the motor with a lower-spec soft start because it only sees the phase current, not the line current.

If you google "soft start inside delta wiring" you get guite a few hits that have diagrams that will help to see how this is done. This one from Aucom for instance : http://www.aucom.com/tech-topics/mo...ection-what-is-it-and-why-would-i-use-it.html


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## Paulusgnome (Mar 28, 2009)

There is a quite informative document available for download from ABB that has some explanation of inside-delta soft starting : http://www05.abb.com/global/scot/sc...f7fc1256f3a00274038/$file/1sfc132002m0201.pdf

Please see P46 for connection diagram.

While this is a valid way of soft-start connection, it is not without problems. It may not give that much of a saving - it does require six conductors to be cabled from motor to softstarter vs 3 conductors for a line-connected softstart, and in most applications it will definitely require a line contactor where one may not be needed if the soft-start is line-connected. There is a potential reliability headache in that if one of the thyristors in the soft-start were to fail short-circuit, it may damage the motor by single-phasing it. Electricians who have not met this type of arrangement before may struggle to work out what has been done and how it works.

The wisdom here is that we would avoid using this arrangement unless specifically asked to do so by a customer.


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## John Valdes (May 17, 2007)

Paul, I see what you are talking about and that may be what the OP is asking? I don't know. I do know that connecting a motor in this fashion is something I have never done and never will do. Cabling is not an issue as I can always parallel 6 lead configurations to the simple three lead that the soft start uses.


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## JRaef (Mar 23, 2009)

This entire concept offers no advantage other than being able to use a smaller cheaper soft starter. The inherent risks involved however are significant, as pointed out by Paul. I been using and installing solid state soft starters for 25+ years, I NEVER recommended using this method for the very reasons Paul mentioned; it can be very confusing for someone not specifically trained on what it is and how it is connected, plus the risks of losing the motor make the cost savings on the starter size insignificant by comparison.

That said, it has become very common now in elevator controllers and refrigeration compressor controls, two industries that tend to have specialized service technicians who do get that specialized training.

But as to the effect with regards to starting current, it is not really significantly different from regular soft starting, but the soft starter electronics do need to be capable of "knowing" this is what you are doing so that it can compensate for the current being 58% of the total.


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## Motorwinder (Dec 30, 2010)

> Inside delta connection does not increase a soft
> starters rating. However, when connected inside the
> delta circuit of a motor, it is possible for a soft starter
> to control a motor with a FLC greater than that of the
> ...


Hope this helps.


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## Ray Cyr (Nov 21, 2007)

This is a good day, I learned something today  . Thank you for the post :thumbsup:


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