A Mr. Electric Electrical Quiz

[Richard Moore]

I had a quick scan over at Mike Holt's site and the consensus there is that a 3-wire (no neutral) feed is legal if only 240-volt loads are to be used. Not the smartest idea, but not breaking any codes. They do say it would be good practice to label the sub-panel clearly with something along the lines of "240 Volts Loads Only - No Neutral Available".

[hausdok]

I had a quick scan over at Mike Holt's site and the consensus there is that a 3-wire (no neutral) feed is legal if only 240-volt loads are to be used. Not the smartest idea, but not breaking any codes. They do say it would be good practice to label the sub-panel clearly with something along the lines of "240 Volts Loads Only - No Neutral Available".

Hi, Well yeah, Jim Simmons does say above that it is legal, just not the best idea in the world. Not in so many words but that's what I take away from it.

ONE TEAM - ONE FIGHT!!!

Mike

[randynavarro]

Hi Jim,

He knows I was going to post his quiz on TIJ; so maybe Jim will stop by to see how folks are responding and he'll chime in.

Brandon, I've got a couple ideas. Let me see what I can do about scrounging up a weekly quiz by a plumbing expert.

ONE TEAM - ONE FIGHT!!!

Mike

Hey, we can start with analyzing Mike's plumbing.

Wait. . . are we talking about building pipes or body pipes?

[John Kogel]

I believe all the subpanel branch circuits are 240V, hence no neutral feeder from the main.

1. There are no handle ties on any of those breaker handles.

Actually, there are. They're the little grey things on every other breaker handle.

2. The bending radii on the feeders is way too sharp.

I'm sure that's a fault

.

3. Both feeders should exit and enter thru the same knockout. Why? Because I've never seen it done any other way, until now.

When the conductors run together, their electro-magnetic fields cancel each other out. When they're run separately, the fields remain intact. If you pass a single wire through a metal plate and run current through it, these fields can cause the metal to heat up. Its the same reason why we want both wires in a knob & tube circuit to enter a box through the same hole.

4. All the white wires should be marked black or red. (But that is a newer code rule, I believe, so does not apply if this is an old installation.)

I suspect that the rule requiring the re-identification of white wires in this situation is quite an old one. I know it was required in the '47 NEC. Even so, it seems to have been one of the more widely ignored rules.

Yeah, Mr Electric is ignoring it.[]

5. They are using the neutral bus at the bottom, bonded to the panel, for a grounding bus. This is a poor choice, but I don't know if there is a NEC rule that addresses this.

I don't know of one, but there might be something in the manufacturer's literature. Unless the panel someday needs to have a neutral added, I can't imagine how it would be a problem.

- Jim Katen, Oregon

It only becomes a problem if they install that neutral feeder, eh?

[Kyle Kubs]

240v only with no grounded conductor is extremely common in commercial/industrial work. But then again, your not likely to have Gommer buy the property in five years and start playing electrician.

The induction heating thing is what you guys should have picked up on right away.

Saw this at a house I inspected recently for a kid, and I mean still dripping wet, kid, that was a little too boisterous about being an engineer. Asked him what kind and he said electrical. So I pointed to this in the basement

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and waited without saying anything to see what his response would be. He got a bewildered look on his face until I asked "so where do you think the other conductor of that K&T circuit is about now?" - He didn't know what Knob & Tube wiring was... What the hell do they teach in electrical school these days?

[Norcal]

A couple of things: There are handle ties on the 20A twin breakers they are a Zinsco/Sylvania handle tie BTW, & whoever put in the sub did not bother to use a recognized conduit or cable system for the feeders.

[Marc]

He got a bewildered look on his face until I asked "so where do you think the other conductor of that K&T circuit is about now?" - He didn't know what Knob & Tube wiring was... What the hell do they teach in electrical school these days?

A wiring course in an engineering curriculum would be badly misplaced. No engineering graduate is ready for any line of engineering work without additional specialized education, done pretty much on his own and at his own initiative. It's like HI work....'train thyself'.

Marc

[John Kogel]

I see the clipped end of one of the K+T wires sticking out from the splice, and the other one is spliced to the white neutral. That's all I can tell from that pic.

We had "Electric Plus" here for a while. 240 v baseboard heaters on a separate circuit with their own meter, no neutral feeder installed in the subpanel. They didn't want people tapping off to run lights and outlets.

[Kyle Kubs]

He got a bewildered look on his face until I asked "so where do you think the other conductor of that K&T circuit is about now?" - He didn't know what Knob & Tube wiring was... What the hell do they teach in electrical school these days?

A wiring course in an engineering curriculum would be badly misplaced. No engineering graduate is ready for any line of engineering work without additional specialized education, done pretty much on his own and at his own initiative. It's like HI work....'train thyself'.

Marc

I understand where your coming from with that but, for crying out loud... Do they at least talk about those old guys, what were their names? Tesla & Edison.. I mean I know we're getting close to plasma conduits and all but I've always thought the history of a thing was an important place to start on how we got to where we are now. Hell, at least give it an honorable mention.

[Douglas Hansen]

Echoing Marc's comments, we have lots of different meanings for the term "electrical engineer." When I lived in Silicon Valley, the term typically was used by folks who were involved in semiconductor or software design or fabrication. None of the folks whose job description had that title were licensed Professional Engineers.

The few licensed PEs with electrical specialties at a facility like Intel are involved in facility maintenance and design, not in the design of the products made by Intel.

In the years when I traveled the country teaching electrical code, I often had licensed PEs in my classes. I would ask them how many courses they took on the National Electrical Code as part of their curriculum or prior to becoming licensed, and the answer was always zero. Interaction with our world is, as Marc said, something that happens after you have the letters after your name.

Douglas Hansen

[hausdok]

Hi Douglas,

It's good to see you once more stopping by, Old Friend. How's married life treating you? Hope we see more of you.

ONE TEAM -ONE FIGHT!!!

Mike

[Kyle Kubs]

I guess that shouldn't surprise me. It still does, but I guess it shouldn't.

[Kyle Kubs]

Hey Mike,

How does Doug have a "joined date" several months earlier than you? I thought you were the big cheese around here?

[Bain]

I guess that shouldn't surprise me. It still does, but I guess it shouldn't.

I've quizzed engineers for whom I've checked out houses. Civil engineers--who typically wind up being "structural" engineers--aren't taught anything about building codes or most of the stuff we look at every day. Like the EEs mentioned by Douglas, structural engineers are typically autodidacts, as well.

[Chad Fabry]

I've quizzed engineers for whom I've checked out houses. Civil engineers--who typically wind up being "structural" engineers--aren't taught anything about building codes or most of the stuff we look at every day. Like the EEs mentioned by Douglas, structural engineers are typically autodidacts, as well.

I almost made it through the day without consulting Merriam or Webster.

The soughing song of pages falling from M to A brought relief from my ignorance.

[Tom Raymond]

Civil engineers are the worst. I think the extra education is to guaranty that they don't know anything.

I worked for one once who insisted on building an adjustable table for a huge sissor arm saw so we could cut common angles on D logs for gable ends. He spent a week bolting index plates to the floor and drilling holes, then moving them when the angles were wrong, then building screw jacks to accomodate the floor that was less than level. When I asked him why we couldn't just use the pivoting base on the saw to set whatever angle we wanted, he insisted that it would never work.

[Kyle Kubs]

I've quizzed engineers for whom I've checked out houses. Civil engineers--who typically wind up being "structural" engineers--aren't taught anything about building codes or most of the stuff we look at every day. Like the EEs mentioned by Douglas, structural engineers are typically autodidacts, as well.

I almost made it through the day without consulting Merriam or Webster.

The soughing song of pages falling from M to A brought relief from my ignorance.

And you couldn't tell everyone else what it means? Now I have to look. [:-paperba

EDIT: Now that's ironic.

[hausdok]

Hey Mike,

How does Doug have a "joined date" several months earlier than you? I thought you were the big cheese around here?

Nope, I'm not a "big" anything. Junior grade janitor in training who's on probation is more like it.

ONE TEAM - ONE FIGHT!!!

Mike