Electrical

Last Updated:18 December 2009

The last of the subassemblies to be dismantled is the electrical system.  The primary electrical components in the assembly are:
-On/Off Switch -Main Distribution Panel
-Worklight -Blade Welder
-Main Power Input Safety Switch -Thermal Cutout
-Motor -Blade Grinder

The blade welder is a mess, and not wired to anything.  I've set it aside for possible restoration at a later time.
The blade grinder is simply missing - it's electrical connections were cut away at some point.

The remainder of the system is present and, from an electrical standpoint, in what I would call "impending fire" condition.  There's certainly nothing particularly "wrong" about wire from the early 40s, but all the electrical connections are coated with such a layer of oil, grease, and flammable dust that their condition may best be described as "get the marshmallows ready".

Aside from the remarkable paint job (remarkably horrifying, that is), notice someone took the time to make a convenient little "purse hook" so the operator has a nice place to store his handbag whilst on the job.  Hopefully it's an asbestos purse.

That cover assembly shouldn't be all bent up and mangled.  Note the thermal cutout mounted below the distribution box is being held in place by its wiring (difficult to see here if you don't know what you're looking for).  Speaking of the thermal cutout, the cover has been lost to history.  That means the wiring is simply exposed.  During operation, there's 208v 3phase running through that cutout without any protection against arcing whatsoever.

In the picture on the left I've labeled a few things that have nothing to do with the electrics, but are convenient to label since they're easy to see.
 
Here's the safety switch.

This is where house power is wired into the saw.  It's in excellent shape, other than the flammable dust pile sitting at the bottom.  It was "union made" by the General Switch Corporation in Brooklyn, NY.

It's not clear whether this box is original.Some things make it look like a later retrofit, some things make it look original.  I've seen lots of pictures of other Doall bandsaws from the same era as this one; some have a different box at this location, some have no such box.

More than likely, the box was a custom-install based upon code requirements in the specific location at which the saw was in operation.

Here's the on/off switch (shown with the cover removed):
This was made by Cutler-Hammer, which is now owned by Eaton.  The most amazing thing about the switch is the label I found inside the box, in perfect condition.  It indicates a build date of July 1940!  And it still works!

I can only imagine how many hundreds of thousands of cycles this thing has seen in 65 years.  The switch on my 2003-built Delta Shopmaster drill press broke in less than 2 years, after maybe 500 cycles.  This is a real piece of history.  I find it interesting that even in 1940 they printed "Made in U.S.A." on things.  I would have thought that unnecessary - wasn't everything made here in the US back then?  I guess not.

Here's an electrical schematic for the original motor and light portions.  Since the blade welder and grinder were cut out of the system by a previous owner, I wasn't able to determine the original wiring configuration for those components.  I do know both the welder and grinder were single-phase 220v components, so if I ever find replacements they'll be simple to rewire.




Reassembly

Here's the new electrical plans.  Note that the wire labels "U", "V", and "W" indicate physical labels applied to those wires as they were installed for easier identification.

The new arrangement represents a simplification of the original design and a slight increase in safety.  Whereas the old design uses a 3-pole switch to turn the motor on and off, this new design uses 2 simple momentary pushbuttons to actuate a contactor.  This is marginally safer, since full motor current is no longer carried to the switchblock, and in case of a power outage the saw cannot restart when power is restored.

Note the safety switch has been eliminated, and the entire electrical system now fits within the main distribution housing, as DoAll originally intended.

Also note the incorporation of an hourmeter, which will permit more accurate preventative maintenance.

Main power is provided via 30 amp 10/4 SOOW service cord carrying two hot poles (red and black), one neutral line (white), and a ground.  Power transfers to the main bus using an Amphenol MIL-spec circular connector rated to at least 46 amp.

Internal main power distribution is carried by 8 ga. stranded THHN (rated to at least 70 amp).  Secondary power (for the hourmeter and contactor coil) is carried by 16 ga. SXL stranded wire.

The new motor provides its own internal thermal protection, so the reader will note the absence of any external protection.  Power connection to the motor is via an Amphenol 97-3106A-20-4S plug and 97-3102A-20-4P box mount receptacle.  This is rated to only 23 amp, although the wiring harness is rated to 70.  The motor is internally wired using 16 ga. wire.

I decided to reuse the original-equipment fuseblock rather than implementing a new circuit-breaker arrangement.  There's no point in re-inventing the wheel when the fuses work fine and are conveniently sized to fit precisely within the main junction box.

This system was tested 20 June 07 and functioned precisely as designed.






At left are a couple photos of the implementation of the wiring schematic.

The first minute registered on the hourmeter (which actually reads minutes rather than hours) occurred at 11:36 pm on 6/21/07.  This was during an electrical test, and the motor wasn't actually connected.  The meter will record 99999 minutes before rolling over, which works out to almost 1667 hours.  It almost certainly won't roll over during my lifetime.

A ground line is provided to and connected at the motor case, but I haven't connected it to house ground yet.  I can't decide whether it's safer to ground the machine or not.

What is the purpose of a ground connection?  It's to ensure that if there's a short, the path of least resistance to ground is not through a human.  But what many people fail to consider, is there's a tradeoff to grounding a system: it provides an enormous path to ground through your body if you should happen to come into contact with one of the hot poles and then touch any other part of the machine.

What's more likely to happen: I accidentally touch one of the hot poles, or one of my wires comes disconnected and contacts the saw while I'm barefoot?  I personally have tremendous (perhaps misplaced) faith in my own wiring, and find it exceedingly unlikely that a wire would break in such a way as to cause a direct short to the machine shell.

By that logic, therefore, it's safer to leave the machine ungrounded.

With an ungrounded machine, if one of the hot poles (and it must be exactly one pole - both poles would simply trip the breaker) were to find a short to the shell, I stand the risk of electrocution only if I provide a good path to ground.  Rubber-soled shoes make excellent insulators.  In fact, I argue the only way I'd be harmed in this example is if I were standing in the rain barefoot at the time of the short.

Update 12/18/09
After considerable thought on the matter, I decided to ground the machine.  It occurred to me that with an ungrounded machine an internal short in the motor could electrify the shell, and then anyone grounded who touches it would be fried.  This is highly unlikely, but perhaps more likely than the possibility of touching one of the hot lines and the shell at the same time (thereby providing a path to ground through the body).  I'm still not convinced this is any safer than running ungrounded, but I figure it can't hurt.  In addition, if there were an internal short in the motor or a wire broke somewhere in the system and touched the shell, a fuse would trip almost instantly.