Overload relay inside of fused disconnect switch

[masterelect1]

Has anyone been exposed to a 3 phase thermal overload relay installed inside of a fusible disconnect(3 pole) switch?

Is this a permissable installation without being UL approved. I have been on the Industrial side for the last 25 years and have never heard of nor have I seen this type of set-up..

Here is a typical situation: a 480v 3ph fan on the roof of a commercial bldg. is being supplied directly from the power panelboard with no control point and no overload relay. There is a fusible disconnect switch within sight of the motor. Obviously,there is overcurrent protection at the source and another level of protection is called for at the FDS. A real example would be a 3HP fan (4.8 amps) with 20 amp circ.brkr. at the panel and a fusible disconnect sw. at the motor which according to the plans is to be fused @ 20 amps. As a result of my raising a concern with the designer about this, the info was passed down to me that a FDS would be installed with a built in OL relay. The fact that I have not been exposed to this does not make it incorrect but it does however raise questions with me. Another issue I have is that civilians will have to go into a distribution panel and turn on/off the fan as needed since there is no control point other than the CB or the rooftop FDS.
Is there something wrong with this picture.

Thanks in advance for your input,
John

 

[jim dungar]

If your FDS (the one within site of your motor) is HP rated and has 6A (max) fuses installed then no additional overload protection would be required.

An individual OL relay must be HP rated or else it can not control the motor directly.

I agree that a manual motor starting switch would be preferred over having to regularly operate a distibution panelboad breaker.

 

[FNCnca]

What is the overload relay turning off, if an overload happens?

 

[masterelect1]

What is the overload relay turning off, if an overload happens?

The OL relay would be shutting down the motor. My concern is that an OL relay inside of a FDS is not standard practice. I am used to dealing with a "bucket" at an MCC or with a combination starter that will stop it's functional use if the OL relay trips (opens the control ckt.) and entering the Combo Starter does not endanger the person doing so.

 

[mdshunk]

The OL relay would be shutting down the motor. My concern is that an OL relay inside of a FDS is not standard practice.

I don't get it.

What you're describing sounds like a regular, ordinary, "combination motor starter". No?

 

[jim dungar]

...entering the Combo Starter does not endanger the person doing so.

Why do you think "entering" a combination starter is safer than entering an FDS?

Unless remote control is required I would look at adding a lockable manual starter instead the "local" fused disconnect.

 

[quogueelectric]

Combination Starter

Combination Starter

What he is describing is a homemade combination starter where someone has put a heater section in the gutter space of the fds.
I have seen them out there and I have seen both good and bad installations. What the poster is asking is if it is legal.
In my opinion probably not but if you nippled it into a pullbox alongside the fds or mounted it in a factory enclosure next to yhe switch I dont see why not.
I used to work for carrier doing building automation exclusively for 2 years and sometimes it is not the installers fault that the controlls were added in a step and fetch manner.
Sometimes you have to add timers and relay interlocks to keep within the designed sequence of operations in a 50 year old motor starter and if you make one mistake you can blow the contacts off of an irreplaceable starter. You break it you bought it rule.

 

[masterelect1]

I don't get it.

What you're describing sounds like a regular, ordinary, "combination motor starter". No?

This is definitely not a combination starter !!
What it is, is a concoction of FDS and an OL relay which will be fitted into the FDS. There is no control relay or motor contactor. Strictly a manual start set-up i.e. turning on/off @ the pnelboard; in other words, "a cheapo installation" Having worked Industrial for the last 25 yrs., I have never seen such a "cheap" way of doing something and I am unsure of the legality.

 

[masterelect1]

Why do you think "entering" a combination starter is safer than entering an FDS?

Unless remote control is required I would look at adding a lockable manual starter instead the "local" fused disconnect.

I don't - sorry I phrased that incorrectly - what I meant was that most combo starters have an external reset button which does allow resetting of the OL relay without opening the door .

 

[davidr43229]

There is no control relay or motor contactor. Strictly a manual start set-up i.e. turning on/off @ the pnelboard; in other words, "a cheapo installation" Having worked Industrial for the last 25 yrs., I have never seen such a "cheap" way of doing something and I am unsure of the legality

I am in agreement with this statement. IMO, if there is a UL on the disconnect, you have certainly voided that. Overload protection is taken at the point of referrence of 4.8amps.
You did not mention of the amperage or Class of the fuses, within the fused disconnect "within sight" of the motor. If the fuse is sized at 125% (or the next size smaller) of this 4.8 amps, the newly installed overload is not needed, per NEC 430.55, 430.57 & 430.90.
Your 20 amp CB is there to protect the wire only. Another 20 amp fuses, serves no purpose other than to cause confusion, in this example.

Another issue I have is that civilians will have to go into a distribution panel and turn on/off the fan as needed since there is no control point other than the CB or the rooftop FDS.
Is there something wrong with this picture.

You are also correct OSHA 1910.334 and the NFPA-70E forbid this, unless the civilians are qualified by the military are not permitted to access nor reset the overloads.
Just my $.02