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#153211 10/15/06 12:56 AM
Joined: Feb 2003
Posts: 288
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Notice how that meter is wired.

120V A-base meters have one current coil, connected between the two outside terminals. The neutral may run across the two inside terminals, or it may be pigtailed. It doesn't really matter, since these terminals need not carry the neutral current.

But here, it looks like the hot(?) goes across both line terminals, and the neutral(?) is pigtailed and jumpered across both load terminals. This must be a 240V A-base meter, but I don't really get how it's wired. I know there is a way to hook up a 240V meter to work on a 120V circuit, but I don't know what it is. The 1961 Sangamo manual doesn't mention it. I suppose you could open the test switch; that would allow you to run both current coils in series, while keeping them isolated from the neutral connection to the voltage coil, but then how would you terminate the neutral? There's no lug for that!

The few two-wire services I've seen have had 240V meters, since the meter would have probably been replaced sometime in the last 40 years, when no 120V meters were available.

OK, now that I look at the pic again, the wire that I thought was the hot ends up on the right-hand terminals of the branch-circuit cutouts, where the white wires of those two modern romex runs are terminated. Can we assume that those white wires are connected correctly (at least according to modern practice), as they bypass the fuses? For that matter, can we assume anything, not being able to hold a voltmeter to a photo?

(One thing that we can see is not connected correctly is that 12/3 homerun. The red and black are connected to separate fuseholders. This is a multi-wire branch circuit, fed from a 120V service!)

I have run a 240V meter on 120V before, and it seemed to register 20% less than the actual demand. It was for a public display, so accuracy wasn't an issue. It just had to turn visibly.

#153212 10/15/06 09:52 AM
Joined: Nov 2001
Posts: 273
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yaktx,the 120 volt meters have a jumper on the second & third terminal. one of the potential coils leads hooks to the first screw on the left then the other to the jumper. on the 120 volt meter yu have only one current coil.the 240 volt meter has two current coils,the potiental coils leads are hooked to the first two screws.the current coils are arranged so that one of each is hooked on the first two screws,then ends on the last two.you are correct about a 240 volt meter being slow on 120, but usually this is not a problem for some people.the meter in this thread is hard to say looks to be a 240 volt unit possibly. most A base meters are lie on the left & load on the right.but there are a few exceptions with some of the old westinghouse meters.

#153213 10/17/06 12:13 AM
Joined: Feb 2003
Posts: 288
Y
Member
Thanks, Circuit Man.

I figured that out after posting this.
I was wrong about the Sangamo manual; the method of connecting a 240V meter for 120V is on page 50. You open the test switch and hook the neutral to it with a fork terminal, then the hot goes across both current coils in series. So you would see a jumper between terminals 3 & 4, and the neutral pigtail is actually terminated separately. That appears to be what we're seeing in this pic.

#153214 10/17/06 12:17 AM
Joined: Feb 2003
Posts: 288
Y
Member
Interesting that the mains fuses before the meter are not is some form of sealed enclosure.
Couple of alligator clips could yield in free power tapped off.


No doubt this practice was very widespread, especially since these meters were almost always inside the house. When the meter reader knocks, scramble downstairs and remove the jumper first...

See page 52 of Hard Times by Studs Terkel (paperback edition).

#153215 10/17/06 06:17 PM
Joined: Aug 2001
Posts: 7,520
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I seem to remember us having a discussion about double-pole fusing and when the NEC disallowed it. I can't rememebr what the answer was though -- Late 1920s/early 1930s?

#153216 10/17/06 11:30 PM
Joined: Feb 2003
Posts: 288
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Member
I seem to remember us having a discussion about double-pole fusing and when the NEC disallowed it. I can't rememebr what the answer was though -- Late 1920s/early 1930s?

It was illegal to fuse neutrals of multiwire systems by 1923, possibly several years earlier.

As for single-pole branch circuits, or two-wire services such as this one, at some point it was thrown to the AHJ to decide. Many of us have had the experience of ordering a disconnect and having to specify that it come with a "solid" neutral (like, what other kind is there?). This is because, in the '30s, there were two types of equipment, those with solid neutrals, and those with fused.

I have every NEC from 1940 to the present, and I also have a Terrell Croft volume containing the entire text of the 1923 NEC (sort of an early "Handbook"). The '23 NEC clearly disallowed fused neutrals for multiwire systems but allowed them for two-wire circuits.

From 1940 to 1953, this is the AHJ's call.

The 1956 NEC contains language similar to today, i.e. 240.22 in the 2002 NEC.

My sense is that fused neutrals became markedly less common after the mid-30s. I still have one of those 2-circuit, 4-fuseholder porcelain cutouts. I found it in a long-abandoned barn in Connecticut ten years ago. It was enclosed in a manufactured cutout box, and the wiring was all Type AC cable, I wanna say TW insulation although I can't remember. If it were TW, that means probably 1948 or later. The neutral fuseholders puzzled me to no end!

#153217 10/21/06 06:07 AM
Joined: Aug 2001
Posts: 7,520
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A similar move to solid neutrals occurred here in Britain, although I'm not sure which edition of our Regs. finally "outlawed" the practice. It may have been as late as the 12th edition (1950) or 13th edition (1955). There were certainly still a good many pre-war double-pole fuseboxes in use, particularly on lighting circuits, as late as the 1970s.

#153218 10/21/06 06:42 AM
Joined: Dec 2001
Posts: 2,498
T
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In Austria all that happened A LOT later. I think that fused neutrals are even still allowed today, even though they aren't as common as they used to be, since breakers that fuse the hot and switch the neutral are very common by now.

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