You will likely have to change the breaker as many of the breakers used in starters are instantaneous only and can only be used as a part of a listed combination motor starter.

I understand what you are saying, what if it is a thermal magnetic type?

Trying to cover all bases since I am bidding a project this week with this

combination.

If it is a thermal magnetic breaker of the correct rating to supply the soft starter, I don't see any issues. However, you are modifying a listed assembly and your AHJ may have an issue.

Typically no "thermal" and that's the problem.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

Mr. DonQ (Electrical)(OP)9 Jul 23 16:51
" ....Does anyone know if an existing across-the-line motor starter inside a motor control center bucket can be changed to a 'soft-starter' without having any issues with NEC?...."
I look at it this way besides the NEC requirements consideration.
1. The existing breaker with magnetic only or with thermal magnetic is fine, as the Soft stater (SS) is equipped with thermal over-load with programable Class.
2. There shall be a contactor* ahead of the SS. Attention: The contactor* acts as an isolating switch when the SS is on stop state, where the SS motor terminals including motor terminals are "life! danger to touch" .
3. The SS shall be installed vertical. Observed the top/bottom and side cooling clearances and the volume of cooling air.
4. SS would require bigger bucket say > 3 time the size and say 2 time the weight of a DOL starter. Possible solution is to break up say breaker + contactor* in a different bucket. The other bigger bucket houses the SS starter in vertical position. The output of the breaker bucket is connected to the input of the SS bucket through external connection. This is to ensure/enable that the two buckets can be removed individually.
Che Kuan Yau (Singapore)

If the AHJ has an issue with me modifying the listed assembly what would be a good option?
The customer wants a soft-starter on the existing pump.

Quote (che12345 )

1. The existing breaker with magnetic only or with thermal magnetic is fine, as the Soft stater (SS) is equipped with thermal over-load with programable Class.

It is not permitted to use the magnetic only breaker to protect the branch circuit that supplies the soft start. The only permitted use for such a breaker in the NEC is where it is part of a listed combination motor starter.

Quote (DonQ )

If the AHJ has an issue with me modifying the listed assembly what would be a good option?
The customer wants a soft-starter on the existing pump.

if the existing starter bucket is the only power source available, you could get a new bucket with a thermal magnetic breaker. Even if if the MCC is obsolete there are panel builders that can build a listed replacement bucket with a thermal magnetic breaker and no starter.

Thanks for your help!

For bidding purposes, I'd get a price for a new bucket from the MCC manufacturer. If you get the job, you can try to find a less expensive solution. But in the end, I'm not sure you'll save that much, unless you are donating a lot of time.

A tip when asking for quotes.
We wanted to add a new MCC section.
The manufacturer quoted us a price around $20,000.
My boss sadly told me that price had killed the project.
I suggested that we had been quoted replacement price.
I suggested that I could match up a section of any manufacture MCC and cable connect it to the existing lineup.
I suggested going for competitive bids and stressing that this was to be new construction, not parts for an existing MCC.
The competitive price dropped to around $5000 and the project went ahead.
If you emphasize that you need a competitive bid and are not locked into one manufacturer, you may be able to buy a complete bucket, ready to plug and play for a very good price.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Quote (waross)

If you emphasize that you need a competitive bid and are not locked into one manufacturer, you may be able to buy a complete bucket, ready to plug and play for a very good price.

I did a couple of projects where a listed replacement bucket was actually cheaper from a third party than from the OEM.

Aside from the breaker issue (which is a critical factor), there are other important issues to consider...

1. You cannot modify an MCC bucket and maintain the NRTL (UL) listing of the bucket, then the way MCCs work is that if any bucket in an MCC is not listed, the entire MCC listing is voided. NRTL listing of the unit will be important, either because the AHJ (inspector) will want to see it, or your company insurance policy will likely require it.
2. There is a 99% chance that a unit space for an ATL starter will not be large enough to fit an equivalent Soft Starter. Ask the MCC mfr what the Space Factor is for a unit with a Soft Starter of that size, you will likely see a significant difference. Heat rise in MCC buckets is an important factor, regardless of the listing status.

To the other point about getting a quote, my experience is that if I need more than one bucket, I get a price on a "new" MCC as if it is a new project, not an "add on to existing". Your cost for a new MCC with those buckets in it will be less than the separate replacement buckets, and it will be shipped in what I call "handy steel shipping container" that you can throw away or find some other use for. MCCs are "loss leaders" for the equipment manufacturers, they lose money on them most of the time. So the plan is to make it up on the replacement or add-on units, knowing that you are "locked in" once you have their MCC. But any time there is a "new" MCC project, they are priced to beat the competition; whether there really is competition or not is something you keep to yourself. Even if I only need the one new bucket, I will sometimes throw in a couple of feeder breakers or starters to have around and spares. It still often comes out cheaper.


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