Should I use starter/ol combination for 2 fan units

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I have two cooling fan units that someone else wired up that is definitely not code. There is one disconnect in sight of the units disconnecting all three. The MCC is not nearby, which contains the starter (and breaker)

Unit 1, 1.5HP and a 2HP 3PH motor
Unit 2, 2 HP Motor These are all 1800 RPM.

I need to set a box and it be code. So... I plan on

2 size 0 AB 509 starters
1 equivalent overload relay for second motor of unit 1 (the 1.5HP)
1 500VA control xfmr 480/120
2 3 pole fuse blocks
1 2 pole fuse block for xfmr
1 Hoffman style enclosure

But, to be code I think I will still need a disconnecting means (breaker) inside the panel. I think the primary of xfmr will need to be fused.

Questions,
1. Must I have a disconnecting means inside the panel or can I use the existing external 30A disconnect to feed the enclosed panel

2. I have used overloads to protect second motors on same piece of machinery without a seperate starter, coming off bottom of contactor to feed the second overload. Is this code or must I have a complete separate controller (starter)?

3. I considered AB supplementary breakers to protect the two motor starter circuits, but with the xfmr needing fuses and the disconnect inside the panel (?) and since whatever disconnects line from starters must disconnect xfmr I think fuseholders and one breaker(as disconnect) would be better looking and code?
 
They do not have internal protection (ol's) The best thing would be to run another set of leads from the mcc, but mcc is full. Also, the guy in charge of our electrical dept. has instructed me to fix it at the motor area. I am still fuzzy though on whether on the unit with two motors (one is 2hp, other 1.5) can I just use one starter sized for fla of both or one starter AND another separate ol relay for second motor, or two complete starters (this would obviously be the most expensive and I would like to avoid, but still need to be code). Then another starter for the other unit's motor which is also 2hp.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
They do not have internal protection (ol's) The best thing would be to run another set of leads from the mcc, but mcc is full. Also, the guy in charge of our electrical dept. has instructed me to fix it at the motor area. I am still fuzzy though on whether on the unit with two motors (one is 2hp, other 1.5) can I just use one starter sized for fla of both or one starter AND another separate ol relay for second motor, or two complete starters (this would obviously be the most expensive and I would like to avoid, but still need to be code). Then another starter for the other unit's motor which is also 2hp.
If it's OK for the motors to come on and off at the same time, one contactor and 2 overloads is fine. But you MUST have a separate OL relay for each motor. You just then wire the aux contacts of the OL relays in series to the contactor coil.

As to the disconnect, one disconnect is fine, again as long as it's OK to shut down and lock out both motors if you want to work on one. But if you must keep one running if you are working on the other one, then you MUST have a LOTO capability for each separate motor.

The SCPD can, under the right circumstances, be one device protecting both circuits. But you must look at the short circuit (instantaneous) trip ratings of a circuit breaker or the short time clearing ratings of a fuse to determine if you are providing proper winding protection as per section 430. The separate OL relays will provide the long time thermal conductor protection, but you can still get in trouble with the instantaneous ratings. Usually the only time you can get away with that is with smaller motors such as yours.

A better all around solution is to use the IEC style "Motor Protection Switches". These are UL listed as "Manual Motor Starters", but typically also carry a "Group Fusing" rating for applications exactly like this. They are the SCPD and the OL and a disconnect device all in one. So you can have one main CB or fuses ahead of your circuit, one contactor (again, if they turn on at the same time) and 2 MPS devices feeding each individual motor. Then if you do need to be able to run one while working on the other, you can get external through-the-door operating handles for the MPSs.
 
I have had (some) experience with IEC Siemens and AB controllers you mentioned. I considered these too, as space requirement is a lot less. But, I would need three (although you stated two for each motor???) I havent seen just an overload relay of this type.

Also, the other problem is fact that per NEC, since I will have xfmr in enclosure, whatever device is used to disconnect power from starters will also have to remve power from the xfmr ( The way I interpret it) I would prefer to fuse the primary of the xfmr and consider using a breaker as disconnect device which then will go to individual fuses for xfmr. I assume I would still need fuses for the IEC combination starters or no?

Would using IEC in this situation likely be a cheaper solution?
 

benaround

Senior Member
Location
Arizona
lonewolf,

You are making a project out of this and you don't have to. The feed from the mcc is all

the control you need, they all come 'on' together they all go 'off' together. Out where the

motors are run the mcc feed into a j-box, come out of the j-box 3 times to 3 manual motor

overload switches, install the proper sized o.l.'s in each, out of each switch tie in your fan

motor, done.

----j-box------1- manual motor overload switch---------1-motor
. l
. l---------2-mmos---------------------------------2-motor
. l
. l---------3-mmos---------------------------------3-motor
.
hope this helps.
 
Last edited:
Benaround,

so what you are saying is that I DONT need separate controls even though there are two physical units (machines) out there (art.430.87). It also sounds from your post that I don't need a disconnect (ie. breaker) inside the j-box. I interpreted code (art.430.74) that disconnects should be provided for all circuits, but I assume that the MMOS would take care of that, as long as I dont have a control power xfmr.

I guess my question is now whether or not I need separate controls based on the fact that I have two separate units (430.87), albeit they are side by side. I personally don't care whether unit 1 and 2 come on together or not, as they have for a long time.
 
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