Industrial load calc

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mic

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Our equipment requires a 480V feed to a breaker panel which services the following:

1. Transformer loaded with both continuous and intermittent loads.
2. Intermittent motors.
3. Two HVAC systems (both considered continuous)
4. Power converter (continuous)
5. Heating coil.

I am calculating the total load of the equipment so the customer can provide an appropriately sized feed(fused). Should I do 100%*(intermittent load) + 125%*(continuous load) OR should I do 125% of the total load since it is a single piece of equipment in the customers eyes.

I guess I am trying to determine an FLA for the equipment along with the WSA for sizing the feed and fuse.
 
Re: Industrial load calc

Originally posted by mic:
Our equipment requires a 480V feed to a breaker panel which services the following:

1. Transformer loaded with both continuous and intermittent loads.
2. Intermittent motors.
3. Two HVAC systems (both considered continuous)
4. Power converter (continuous)
5. Heating coil.

I am calculating the total load of the equipment so the customer can provide an appropriately sized feed(fused). Should I do 100%*(intermittent load) + 125%*(continuous load) OR should I do 125% of the total load since it is a single piece of equipment in the customers eyes.

I guess I am trying to determine an FLA for the equipment along with the WSA for sizing the feed and fuse.
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The following is not a "code" answer (meaning it won't result in the least cost), but I am inclined towards the notion that down the road someone will want to hook something else into this panelboard, thus I am inclined to oversize such things. Unless the cost is way out of wack, I'd size it assuming someone will pack the panelboard full of breakers down the road, cause someone will eventually. I hate it when I have to tell someone to run another circuit cause someone saved a hundred bucks a couple years ago.
 
Re: Industrial load calc

When you say "single piece of equipment", do you mean that this is one machine that has all these components in it or process assembly that includes these indivdual units?

Regardless, I tend to agree with the previous post. I would size the service at continuous to get that extra 25%. Would this same service feed any lighting or general purpose needs?
 
Re: Industrial load calc

All of the stated components are part of a large piece of equipment. We manufacture and install the equipment. All the customer has to do is connect the main feed and throw the switch and it is up and running.

Technically the customer should not be adding to or modifying the panel. If they did modify the panel we would no longer be responsible for the load.

My primary goal is to minimize the power feed requirements so the customer can allocate power resources where they are needed.
 
Re: Industrial load calc

Per the code, I believe you would calculate it like this:

1. 100% intermitent loads
2. 125% of continuous loads
3. 125% of largest motor or largest compressor (or maybe both) for starting current.
4. Heating: 100% or 125% depending on the size and use.

Steve
 
Re: Industrial load calc

See article 424 for space heating equipment. I think the branch circuit (wire and circuit breaker) has to be sized for 125% (because a heater is considered a continuous load).

After a second look , I think the 100% sizing is for subdivided loads (424.22) with additional overcurrent protection.

Steve
 
Re: Industrial load calc

Demand Factor Calculations:
NEC 220-10 THRU 220-41

For non dwelling unit:

motors: "100% of all motors plus 25% of the highest motor of the group" (430-24)

Fixed Heating: 100% (220-15)

Transformer: I would suggest 125% of XFMR rating.

HVAC: Typically used 80% of sum of heat and AC nameplates.

For dwelling units it's a whole different ball game.
 
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