Nema plug questions.

Early outlets had a dimple in the contacts to hold the plugs tighter. Then metalurgy advanced, providing springy contacts that provided more pressure while still allowing reasonable insertion pressure. the holes were retain to ensure compatibility with older outlets.

The ground contacts in a 120V NEMA outlet contact two or three sides of the pin, (Depending on the OEM) so as far as the outlet is concerned it is the same.

I cannot tell you why they were used in the first place but they allow the installation of lock out tag out blocks on the ends of cords when servicing larger machines.

-- Tom Horne

Thank you to those who posted answers to my questions. I now have another one. On Ebay at the moment there is a strange receptacle. Both hot and neutral holes are 'T' shaped, like the neutral on 20 A ones; there is no ground, but the hot and neutral are shifted up to the position where they would have to be if there was one. What is the purpose of this thing? It's described as being for replacement purposes only, so presumably it's obsolete. It would seem to be able to take either a 1-15 120V or 2-15 240V plug, but why would you want such a thing? Surely you'd want to avoid plugging something into the wrong Voltage.

My house still has a couple of such outlets, but the slots are centered. I never knew of the reason for the "T" slots. I've never seen anything with a 2-15 plug w/o a ground pin.

Michael Moroney Inscribed thus:

WAG ! Adaptor socket for flat blade plugs. Take either horizontal or vertical flat blades. Maybe !

What is the item number on Ebay?

230566259249

The box shows it as being 125 V 15 A, so I can't see what the horizontal parts of the slots are for.

Did they once use plugs with two horizontal blades for 120V (110V at the time) ? I've never seen any.

That looks fairly modern, unlike mine which appear to be ceramic.

Michael Moroney Inscribed thus:

I've only seen the ones with vertical blades for power usage ! I've seen similar sockets in bathrooms that will take several types of plug, usually for things like electric shavers. The plugs I've seen with horizontal blades have been for telephones, mainly in Eastern Europe.

The outlet is marked, Made in Mexico. I don't see any UL markings on it. Nema 15R is a two wire polarized receptacle. I'm not sure that was made for the US market.

The shaver sockets are made to take various plugs, round pins for most of Europe, shorter fatter round ones for the UK, parallel flat ones for the USA and angled flat ones for Australia.

For normal mains sockets in the USA vertical blades are 120V, horizontal ones are for 208 or 240V. That's for 15A; for 20A the hot blade is as for

15A and the neutral one is rotated 90 degrees. 20A sockets have a 'T' shaped slot for the neutral blade, so they can accept both 15A and 20A plugs, but I've never seen one with two 'T' slots like the one I was asking about. Angled blades are 277V (phase Voltage on a 480V three phase supply), and in theory one horizontal and one angled is for 347V (phase Voltage on 600V supply), but I've never seen one of these.

Those are the only ones that I can remember; if I need to know 30, 50 or 60 A ones, or three phase ones etc. then I have to look them up.

That's just the straight blade ones; there are rather more of the locking type. Thank goodness I'm in the UK; things are much simpler here.

Leviton devices have been made in Mexico for many years now. The description explicitly states it is not UL listed.

That is well known. The same for Eagle and a couple dozen other brands. However, those made for the US are clearly marked with the UL logo.

Then it was likely made for use outside the US. The construction and markings don't meet US reqirements for anything I've ever seen.

As far as their receptacles are concerned, the older ones seem to be made in the USA and the newer ones in Mexico, which suggests that this strange one is not that old. Their lampholders, the main product of theirs that I use, seem to be made in China.

I collect lamps and lighting equipment and have quite a lot of American HID lamps of various types. Many of them are quite different to the ones we have here in Europe, which is why I need strange (for this country) things like E39 and position oriented lampholders, and why I am probably one of the few people in England to have 1 kVA worth of 277 V 60 Hz. power available at home.

What exactly is the significance of the UL marking? Do things have to be so marked to be used in the USA?

ey"

The National Electrical Code is the basic code for the US. It is adopted (s= ometimes with modifications) for most of the country.

The NEC requires, in general, "equipment required or permitted by this Code= shall be acceptable only if approved" (110 2).

Approved is defined as "Acceptable to the authority having jurisdiction."= =20

That is the inspector, or whatever adopted the code. UL listing will work. = Listing by some other major testing labs probably will also. Testing here m= eans samples of the equipment have been tested by the lab to determine if t= hey meet the applicable standard. For switches, receptacles, ... the tests= include many operations of the device, so it not only fails safely, it has= a useful and safe life. Europe, I believe, the equivalent 'listing' proces= s usually means the manufacturer certifies the device meets the appropriat= e standard.

Further, for receptacles, the NEC says the "receptacles shall be listed....= " (406.2-A).

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D We used to call the receptacle you found "t-slots", and they were the stand= ard receptacle used for replacement of 120V ungrounded receptacles. I looke= d in my junk, er.. salvage, boxes and found 4 of them. At least one is UL l= isted.

I think I remember from the dim past one plug on something that had 2 horiz= ontal blades. I suspect that the horizontal parts are for compatibility wit= h real old plugs.

--=20 bud--

These configurations are all standard and well defined. I believe GE has a better, more comprehensive chart but 15 seconds of Googling got me this one.

Each current, voltage and phasing capacity has it's own defined receptical configuration.

I thought they may have been some electrical people here.

The NEC requires, in general, "equipment required or permitted by this Code shall be acceptable only if approved" (110 2).

Approved is defined as "Acceptable to the authority having jurisdiction."

That is the inspector, or whatever adopted the code. UL listing will work. Listing by some other major testing labs probably will also. Testing here means samples of the equipment have been tested by the lab to determine if they meet the applicable standard. For switches, receptacles, ... the tests include many operations of the device, so it not only fails safely, it has a useful and safe life. Europe, I believe, the equivalent 'listing' process usually means the manufacturer certifies the device meets the appropriate standard.

Further, for receptacles, the NEC says the "receptacles shall be listed...." (406.2-A).

================== We used to call the receptacle you found "t-slots", and they were the standard receptacle used for replacement of 120V ungrounded receptacles. I looked in my junk, er.. salvage, boxes and found 4 of them. At least one is UL listed.

I think I remember from the dim past one plug on something that had 2 horizontal blades. I suspect that the horizontal parts are for compatibility with real old plugs.

Josepi,

I have seen many versions of the chart, but none of them shows the configuration that I was asking about, i.e. two 'T' shaped slots.

AFAIK

Underwriters Laboratory approval markings were required to be used in the USA. In Canada it was CSA (Canada Standards Association), only. Now the UL comes with several smaller letters beside it to clarify which country it is approved in. cUL or ULus or cULus (both). Also the governments have both decided to accept reciprocal companies marks for approvals, so that the USA accepts standards from CSA also.

Note UL and CSA are private companies and not affiliated with either government.

As far as their receptacles are concerned, the older ones seem to be made in the USA and the newer ones in Mexico, which suggests that this strange one is not that old. Their lampholders, the main product of theirs that I use, seem to be made in China.

I collect lamps and lighting equipment and have quite a lot of American HID lamps of various types. Many of them are quite different to the ones we have here in Europe, which is why I need strange (for this country) things like E39 and position oriented lampholders, and why I am probably one of the few people in England to have 1 kVA worth of 277 V 60 Hz. power available at home.

What exactly is the significance of the UL marking? Do things have to be so marked to be used in the USA?