Sawmill questions

A

ammklq143

Senior Member
Location
Iowa
Occupation
Electrician
I’m looking for some input on a sawmill. To me, it seems like that would be Class III, Division 1. Does that seem right?

The customer bought a 480v 800 amp genset and is going to use that to power his 480v loads. He also has single phase 120/240v power onsite.

In the mill, he has a 150hp 480v motor and a 50hp 480v motor. He will have some 208v motors also. One 80hp which could be changed to 480v if that works better. One 17hp that could also be changed to 480. One 1hp motor that is 115/208-230v.

For the 50hp motor, I believe he has a controller to start it. The 150hp doesn’t have anything currently. Probably need something other than a disconnect for starting that rather than just slamming it on. What would be the best/cheapest option?

I’d either need to reconfigure the lower voltage motors to 480v or install a step down transformer. Any pros and cons to these?

Lastly, he’s going to have to feed some motors in another building with the genset in the future. It’s right next to the current building. Any suggestions for planning for that for the future to make it easier? Put something out by the genset so I could split it and go into each building separately?

There’s a lot going on here, but if anyone has any suggestions, I’d appreciate hearing them.

Thank you!
 
ammklq143 said:
What would be the best/cheapest option?
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The best option will not be the cheapest.
You should be looking at some type of soft starter with a bypass contactor.

ammklq143 said:
Any pros and cons to these?
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You should wire motors for 480V and avoid transformers when ever possible.

Is this mill just sawing and planning wood, or will it also have sanding equipment.
The very fine dust from sanding is more of a hazard than the coarser saw dust.
 
Usually the 150 will have a delta-wye starter, most of my sawmill experience has been with diesel driven circular blade mills, but I have a band saw mill that I have to reconnect for a customer. Never seen one wired for a hazardous location, and this one is no exception. The control cabinet is a real rats nest, and the ocp for is a single 600 amp breaker, no lower fusing for any motor! It’s going to take a while to straighten out once he sets it up.
 
Hazardous location really depends on some details. Like Jim D said fine dust from sanding is more of a possible hazard than coarse particles from sawing/planing/etc. But even then if you have dust collection system that possibly can be enough to eliminate needing to classify the area at all. What becomes explosive is fine particles suspended in air and in a closed in enough environment that any ignition of such particles would cause rapid expansion and resulting pressure to rupture whatever is containing this mixture. If this activity is happening outdoors, there likely is no hazardous location in most instances.
 
Sawmills CAN end up classified as Class II, Div. 2 in many cases, but that’s not for YOU to decide. They need to TELL you what the hazard classification will be so that you can design the electrical systems accordingly. In most cases though, the sawmill will take steps to AVOID ending up with a Cl II Div. 2 rating, because things get really expensive really fast, including their insurance premiums. One common way they do it is to have a fire /spark suppression system, such as what a company called Grecon provides. Nearly every sawmill I have worked on has a Grecon suppression system. With that, the electrical gear is usually just NEMA/UL Type 12. But again, that’s not an electrical design issue, that’s something they need to decide on then let you know so that you can design the electrical.

Solid state soft starter is probably your simplest easiest option for the larger motors. Simple to install and set up. But technically, if you get closer to maxing out that generator, an RVAT starter has the lowest burden on the source. They are just hard to find readily available and are big and heavy to deal with on installing.

And I agree on trying to avoid transformers for the 3 phase motors, they waste energy and in a generator sourced system, energy = fuel cost.
 
Jraef said:
They need to TELL you what the hazard classification will be
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Key here is who is "they".

Smaller operation, chances are nobody has a clue what you are talking about. Get a little bigger operation, say something that has at least a dozen or so employees and maybe you have more of a chance of insurance stepping in if there is no other AHJ that steps in. Electrical inspector - if one is involved isn't usually qualified to make any such classification either. Some might think they are, others might realize they are not but may still want worst case scenario followed unless someone qualified does determine any classification that applies.

511 to 516 is easy for an EI - NEC tells us what is what. Other classified areas aren't so clear using NEC alone. Typical EI isn't able to enforce much more than NEC plus local amendments though.
 
kwired said:
Hazardous location really depends on some details. Like Jim D said fine dust from sanding is more of a possible hazard than coarse particles from sawing/planing/etc. But even then if you have dust collection system that possibly can be enough to eliminate needing to classify the area at all. What becomes explosive is fine particles suspended in air and in a closed in enough environment that any ignition of such particles would cause rapid expansion and resulting pressure to rupture whatever is containing this mixture. If this activity is happening outdoors, there likely is no hazardous location in most instances.
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They're just sawing the logs and no sanding. The building is open on two sides, so it's not fully enclosed, but closed enough that there will be dust from sawing floating around.
 
ammklq143 said:
They're just sawing the logs and no sanding. The building is open on two sides, so it's not fully enclosed, but closed enough that there will be dust from sawing floating around.
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If the workers do not need to wear respirators, simple housekeeping typically keeps these types of locations from being classified as hazardous. Think of the sawdust that builds up around the motor on a table saw.
 
hillbilly1 said:
Usually the sawmills are in a rural area where permits don’t exist LOL!
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I can agree with that. Then when some incident occurs with injury, loss of life or significant property damage their attorney will try to come after anyone that was involved. If there happened to be any kind of official statement of this being non classified, or exactly what classifications exist and where - then you are better protected from liability if your install complied with those classifications. If anything the liability has better chance of shifting to whoever determined the classifications, or possibly to whoever failed to maintain the installation to those conditions after initial install.
 
kwired said:
Then when some incident occurs with injury, loss of life or significant property damage their attorney will try to come after anyone that was involved.
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Not directly related, but one of my first jobs as an engineer was to investigate why a control system that my employer built for a cardboard compactor had failed to stop when an operator got his arm torn off after getting his sleeve caught. Very tragic situation, and as you might imagine, lawyers were desperately looking for the deepest pockets to go after and I worked for the electrical equipment mfr., so that was us. Longer story short we hadn’t wired anything, so we were not responsible for the glaring mistake (they tapped off of the LINE side of the main disconnect to feed the auger, so when they threw the handle, the auger kept pulling him in). We technically “won” the suit against us, but it apparently cost us over $250k in legal fees, and that was in 1980!
 
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