Wood Mill wiring methods

[kwired]

There donung an ark flash study and will find all AIC ratings to each panel… though I don’t know when.
I could do a rough one to just my location for a rough idea what I’ll have, but I don’t know how to sacking for motor contributions.

Hopefully the motor doesn't contribute very much or the 5kA rating is no good to begin with.

 

[jim dungar]

I could do a rough one to just my location for a rough idea what I’ll have, but I don’t know how to sacking for motor contributions.

Motors contribute about 4X full load current. It takes a lot of HP to raise the fault current by more than a few hundred amps. Motors driven by simple VFDs do not contribute anything

 

[kwired]

Motors driven by simple VFDs do not contribute anything

I'll add load side won't back feed anything into the supply side, front end rectifier won't let that happen on simple VFD's. Might be possible with more complex drive if you intend to feed regenerative energy back into the supply, but even that probably would have some regulation to it for something abnormal like a fault in the motor.

 

[AC\DC]

this is my panel type I have. Call ABB Monday seems like a current limiting and then a isolation transformer my get me down to were I need to be

 

[jim dungar]

this is my panel type I have. Call ABB Monday seems like a current limiting and then a isolation transformer my get me down to were I need to be

If you use a transformer, you do not need the breaker to be current limiting.

 

[AC\DC]

so a transformer does not have a SCCR rating or an AIC rating correct. So I get an isolated transformer with same rating for secondary as primary and get the impedance on the transformer high enough to lower my AIC to below the 5kaSCCR I need- if that’s the case that’s another 5k to the estimate from my looking over the last hour…

After reading I see why you said I don’t need a current limit g breaker…

So is the best way when this comes up to just get an isolation transformer….

Then what happens when power company changes there AIC the thing still blows up lol

Thank you—- saved my but and hopefully make a happy customer.

Would you wait for the ark flash study or just fiqure out your self—- if I wait it’s going to be a year and they may move to someone else. That say screw it lol

 

[Fred B]

Is anything there considered a Class 2 or 3 hazardous location? That might be why everything is RMC, and the couple EMT runs were non compliant add ons some time later?

Saw mill with the dust is considered a class 2 environment. Every mill I've been in, even with a good vac system, has a significant coating of saw dust particles over most of the area, even farther away from the immediate cutting area. In the right air concentrations it can actually be explosive. Usually why the vacuum systems on the large millwork facilities will be outside the main building to limit the more volatile concentrations away from the working area.

 

[hillbilly1]

I was talking to the previous owner of a sawmill in Ohio how bad the wiring looked on a mill I was disassembling, he said there was a lot of mill fires up there.

 

[kwired]

I was talking to the previous owner of a sawmill in Ohio how bad the wiring looked on a mill I was disassembling, he said there was a lot of mill fires up there.

Not necessarily much for explosion events though. Housekeeping activities are possibly a major factor in whether such a facility may need to consider calling it a classified location. Fine airborne dust is what is explosive in nature and is even more so when in an enclosed space as the pressure of rapid combustion is what blows the enclosure out. There is also the possibility of igniting the layer of material that accumulates on heat producing items but a routine housekeeping schedule does help minimize this. At very least there isn't as much accumulation to ignite when you do have an incident. It doesn't need to be electrical items that are the source of ignition, bad bearing on a machine or something similar can do this as well. Many grain elevator explosions (I have more first hand experiences with those applications than sawmills) occurred because of some mechanical failure like a bad bearing in some piece of equipment and the resulting heat was the ignition source.

 

[retirede]

I’d think a sawmill would be pretty low risk since they normally are sawing trees that still relatively high in moisture content. I was in one once and the piles of cuttings were really damp.
As opposed to a wood shop working with kiln-dried stock. Sanding equipment probably emits the most flammable dust.

 

[kwired]

I’d think a sawmill would be pretty low risk since they normally are sawing trees that still relatively high in moisture content. I was in one once and the piles of cuttings were really damp.
As opposed to a wood shop working with kiln-dried stock. Sanding equipment probably emits the most flammable dust.

My thought as well. Though if they never clean up it eventually dries out and some heat producing failure can still be an ignition source, it just not likely to be an explosive event when it starts combustion. But once a fire starts there is plenty of somewhat easily ignitable fuel to keep it going.

 

[hillbilly1]

Not necessarily much for explosion events though. Housekeeping activities are possibly a major factor in whether such a facility may need to consider calling it a classified location. Fine airborne dust is what is explosive in nature and is even more so when in an enclosed space as the pressure of rapid combustion is what blows the enclosure out. There is also the possibility of igniting the layer of material that accumulates on heat producing items but a routine housekeeping schedule does help minimize this. At very least there isn't as much accumulation to ignite when you do have an incident. It doesn't need to be electrical items that are the source of ignition, bad bearing on a machine or something similar can do this as well. Many grain elevator explosions (I have more first hand experiences with those applications than sawmills) occurred because of some mechanical failure like a bad bearing in some piece of equipment and the resulting heat was the ignition source.

A lot of the motors are overfused or not fused at all. The mill I took apart was fused at 600 amps @ 480 volts. That was for everything!

 

[hillbilly1]

I’d think a sawmill would be pretty low risk since they normally are sawing trees that still relatively high in moisture content. I was in one once and the piles of cuttings were really damp.
As opposed to a wood shop working with kiln-dried stock. Sanding equipment probably emits the most flammable dust.

A lot of large mills spray water on the log piles, keeping them wet.

 

[kwired]

A lot of large mills spray water on the log piles, keeping them wet.

Maybe to keep them from warping as they dry out? They are going to begin drying even faster once cut. I don't know enough about kiln drying but maybe they take some other measures to lessen warping once the wood gets there?

 

[jim dungar]

A lot of large mills spray water on the log piles, keeping them wet.

This is often to keep the wood/logs from splitting and checking before going into the machinery and for dust control. Unless the wood is submerged the inside portions are not going to stay wet.

 

[retirede]

Unless the wood is submerged the inside portions are not going to stay wet.

It’s not going to dry, either. A mature log will rot on the outside before the core dries out. Varies somewhat by species. White oak it what I’m most familiar with.

 

[AC\DC]

This isn’t a mill to make two by fours they make a laminated engineered beams so it is pretty dry. They have a kill and everything but that’s inside and I’m dealing with outside.