T-slot plugs and 20 amp appliances?

I've never seen a 20A 120V plug on anything, residential or otherwise. The higher powered stuff is 240V. Something must use them though.

The NEC has not changed in this area. The only time you need the NEMA

5-20 is if it is a single receptacle on a 20a circuit. You can use 5-15s if there are two or more. (a duplex device is two)

| All this discussion of 240-volt appliances has me wondering about the | fairly recent US and Canadian electrical code changes that encourage us | to install the t-slot 20 Amp receptacles in places like kitchens. But | now I wonder why. Aside from providing some indication that the branch | circuit was wired with slightly heavier wire, are there any consumer | products out there that use the 20-amp style plug? | | | I'll have to look to see if I can find the NEC discussions on the rule | amendment that allowed the T-slot plugs. I'm curious as to the | motivation for this.

If you are referring to "allowing" the NEMA 5-20R outlets, they have been allowed for a long time, at least as far back as the 1960's when I first saw one. They are required for a single dedicated outlet that has 20A circuit protection (although arguably, this is pointless). Where a NEMA

5-20R is used, the circuit must be protected at 20A and thus must have a rating of 20A. But you can use NEMA 5-15R on a 20A circuit which has more than one outlet.

The NEMA 5-20R has a T-slot only on the grounded conductor blade. This allows it to fit either a NEMA 1-15P, NEMA 1-20P, NEMA 5-15P or NEMA 5-20P. The NEMA

5-20P has the grounded conductor blade turned 90 degrees and offset outward to maintain the 1/2 inch spacing between the blades. The NEMA 2-20P may also fit but this would have problems if plugged in that way since it would be for an older 240V ungrounded appliance now getting only 120V.

The NEMA 6-20R also has one T-slot, but that T-slot is on the side of the outlet corresponding to the side the hot conductor is on in a 5-15/20. Both conductor slots are hot at 120V relative to ground, but the one on the right when the ground pin is down (left when ground is up) is the one that has the T-slow for these 240V outlets.

The legacy T-slot outlet was an ungrounded outlet that had the T-slot hole for both conductors. I still occaisionally see them around on very old wiring. The intent was to be a single product usable for either 120V or

240V circuits. You can see the risks it exposed. It would not be allowed today, and may not have ever been technically allowed.

Based on the 80% rule and assuming exactly 120V and 240V, appliances could use these plugs for these wattage or volt-amp ratings:

5-15P 1440 5-20P 1920 6-15P 2880 6-20P 3840

Although I would rather use 240V in these (and other [*]) cases, I have seen some appliances with a NEMA 5-20P though I don't recall if any were things you might commonly see in a kitchen.

Is your reference to "encourage us to install the t-slot 20 Amp receptacles" in reference to the NEMA 5-20R?

There is a difference between "encourage" and "allow".

I do not see anything in the NEC 2008 code that encourages or requires NEMA

5-20R outlets on the kitchen circuits (that have to be 20A). They are allowed and in all places I've seen that might be recent installs, are used. As long as the circuit has at least 2 outlets (a duplex receptacle does this), then NEMA 5-15R outlets are sufficient. See NEC 210.21(B)(1) and (3).

The only case where you would be required to have NEMA 5-20R outlets in a kitchen is if you meet NEC 210.11(C)(1) through the use of a dedicated branch circuit for each single outlet, per NEC 210.21(B)(3).

I would actually prefer to use NEMA 5-15R only to meet the minimum kitchen requirements in NEC 210.52, and supplement that with 2 or more NEMA 5-20R on separate dedicated branch circuits. Heavier appliances would thus be kept apart from the multi-outlet circuits. I'd also have NEMA 6-20R for even heavier kitchen appliances like a 2400 watt microwave.

My layout might be like this:

Let me know if you find the rule in NEC you are looking for that allows the T-slot plugs (I think you mean outlets) if it is not NEC 210.21(B)(3).

[*] I'm all for deleting NEC 210.6(A)(2) or at least making it not apply to single family dwelling units.

I think I just replaced on of these. Are you saying that it was desighned to be wired ether to a 120v curcuit (using the standard vertical " | | " plug) or a 240v curcuit (using a "- -" plug)?

Is a "- -" plug standard for 240v? if so what amprage?

Just curious (mine was definatly a 120v 15a curcuit

"Jeff Strickland" wrote

I know about the standard "T" plug for 20 amps. I think phil was referencing to a very old double "T" outlet ie "--| |--" I replaced one like that reciently that I am certain was never hooked up to more than 15 amp along with about 5 other outlets and 3 ceiling lights.

On Thu, 29 May 2008 04:44:38 GMT Stephen B. wrote: | "Jeff Strickland" wrote |>

|>>> The legacy T-slot outlet was an ungrounded outlet that had the |>>> T-slot hole |>>> for both conductors. I still occaisionally see them around on |>>> very old |>>> wiring. The intent was to be a single product usable for either |>>> 120V or |>>> 240V circuits. You can see the risks it exposed. It would not be |>>> allowed |>>> today, and may not have ever been technically allowed. |>>

|>> I think I just replaced on of these. Are you saying that it was |>> desighned to be wired ether to a 120v curcuit (using the standard |>> vertical " | | " plug) or a 240v curcuit (using a "- -" plug)? |>>

|>> Is a "- -" plug standard for 240v? if so what amprage? |>>

|>> Just curious (mine was definatly a 120v 15a curcuit |>>

|>

|>

|>

|> There is a 120v/20A plug that looks like | -- , this is what they |> are talking about. The standard 120V/15A plug has | |, and the 20A |> version has | -- (or -- | ) configuration. |>

| | I know about the standard "T" plug for 20 amps. I think phil was | referencing to a very old double "T" outlet ie "--| |--" | I replaced one like that reciently that I am certain was never hooked | up to more than 15 amp along with about 5 other outlets and 3 ceiling | lights.

That is exactly what I was referencing.

|>> The legacy T-slot outlet was an ungrounded outlet that had the T-slot |>> hole |>> for both conductors. I still occaisionally see them around on very old |>> wiring. The intent was to be a single product usable for either 120V or |>> 240V circuits. You can see the risks it exposed. It would not be |>> allowed |>> today, and may not have ever been technically allowed. |>

|> I think I just replaced on of these. Are you saying that it was desighned |> to be wired ether to a 120v curcuit (using the standard vertical " | | " |> plug) or a 240v curcuit (using a "- -" plug)? |>

|> Is a "- -" plug standard for 240v? if so what amprage? |>

|> Just curious (mine was definatly a 120v 15a curcuit |>

| | | | There is a 120v/20A plug that looks like | -- , this is what they are | talking about. The standard 120V/15A plug has | |, and the 20A version has | | -- (or -- | ) configuration.

If the plug does NOT have a ground pin, then "| -" and "- |" are just the same thing turned 180 degrees. It represents 240V 20A ungrounded. It has a designation NEMA 2-20. A NEMA 2-20P plug will mate with a NEMA 6-20R outlet. It will also mate with a NEMA 5-20R which can be a problem for an appliance that could be a hazard operating on a lower voltage. There is a NEMA 1-20 for 120V 20A ungrounded. It has a vertical blade/slot and one with a short angle on it. It will mate with a NEMA 5-15R/5-20R combination, but not with a NEMA 5-20R-only that is designed to not accept NEMA 5-15P (and not with any 240V outlet configuration).

A more interesting receptacle configuration is the NEMA 14-15R. It accepts both a NEMA 14-15P as well as a NEMA 6-15P. The NEMA 14-15R is a NEMA 6-15R with an added "-" blade above (for ground pin down) the other "- -" blades to add the neutral conductor. I have not seen this manufactured anywhere.

You can see a NEMA 14-15R example in these illustrations for simplex and duplex configurations:

| If you have a 20A circuit that has multiple outlets, you do not need the | T-slot recepticle. | | You need a t-slot recepticle when you install a dedicated 20A circuit. The | T-slot is a visual queue that the power in the wall will operate a 20A | device. If you actually have a 20A device, it must have a t-slot plug to fit | the recepticle.

Note that the above is equally correct for both 120V and 240V configurations.

I still have a couple of these, and for a long time I wondered about the intent of the T slot. House was built in 1940.

The only residential use I've seen are larger window air conditioners. Other large window A/Cs have 240V plugs.

I've seen some commercial computer equipment with these plugs and I have a work bench with a power strip of several duplex outlets. The power cord for the strip is 12/3 with a 20A 120V plug. But neither of these were for residential use.

Interesting. I never knew that existed. I have a duplex recepticle that has a 5-15R on the top and a 6-15R on the bottom. Since the neutral has to be there anyway, they could have added the extra pin easily to the bottom outlet. But as you mention the 14-15R is either rare or nonexistent. (my duplex outlet itself is oddball)

BTW a "face" you don't have is a 347V 15A outlet. It has one horizontal "eye" and one slanted "eye" like the 7-15R. I wonder if it (and the

277V 15A 7-15R outlet) are also merely theoretical or are there devices that actually use them.

On Fri, 30 May 2008 12:47:40 +0000 (UTC) Michael Moroney wrote: | James Sweet writes: | |>I've never seen a 20A 120V plug on anything, residential or otherwise. |>The higher powered stuff is 240V. Something must use them though. | | The only residential use I've seen are larger window air conditioners. | Other large window A/Cs have 240V plugs. | | I've seen some commercial computer equipment with these plugs and I have | a work bench with a power strip of several duplex outlets. The power cord | for the strip is 12/3 with a 20A 120V plug. But neither of these were | for residential use.

So what would you use for a group of computers that need to be connected to power from a single outlet for maximum protection, which use more than the current allowed on a 5-15P plug?

On Fri, 30 May 2008 13:00:36 +0000 (UTC) Michael Moroney wrote: | snipped-for-privacy@ipal.net writes: | |>A more interesting receptacle configuration is the NEMA 14-15R. It accepts |>both a NEMA 14-15P as well as a NEMA 6-15P. The NEMA 14-15R is a NEMA 6-15R |>with an added "-" blade above (for ground pin down) the other "- -" blades |>to add the neutral conductor. I have not seen this manufactured anywhere. | | Interesting. I never knew that existed. I have a duplex recepticle that | has a 5-15R on the top and a 6-15R on the bottom. Since the neutral has | to be there anyway, they could have added the extra pin easily to the | bottom outlet. But as you mention the 14-15R is either rare or | nonexistent. (my duplex outlet itself is oddball)

That duplex is still manufactured by at least Hubbell and Leviton.

| BTW a "face" you don't have is a 347V 15A outlet. It has one horizontal | "eye" and one slanted "eye" like the 7-15R. I wonder if it (and the | 277V 15A 7-15R outlet) are also merely theoretical or are there devices | that actually use them.

That would be a NEMA 24-15R. The 24-20R is a mirror image of it. I have seen the 7-15R duplex in the Leviton catalog.

On Fri, 30 May 2008 12:39:37 +0000 (UTC) Michael Moroney wrote: | snipped-for-privacy@ipal.net writes: | |>The legacy T-slot outlet was an ungrounded outlet that had the T-slot hole |>for both conductors. I still occaisionally see them around on very old |>wiring. The intent was to be a single product usable for either 120V or |>240V circuits. You can see the risks it exposed. It would not be allowed |>today, and may not have ever been technically allowed. | | I still have a couple of these, and for a long time I wondered about the | intent of the T slot. House was built in 1940.

I'm guess they are installed in place. If you ever decide to replace them in the wall, keep the original devices. They could be valuable antiques.

6-15 power cords and switch the PS to 240v

Or multiple 120 VAC circuits, like we do in broadcast studios and CATV headends.

I would do exactly as they did for this workbench, which I bought surplus from a computer company. It has 4 5-20R duplex recepticles for test equipment and what's being tested. I just wanted to point out that such plugs do exist (I've also bought a plug at Home Depot where the blades could be configured like this, although I didn't). These plugs exist in the wild, although for residential use I've only seen them for window A/C units.

On Sat, 31 May 2008 23:20:53 -0400 snipped-for-privacy@aol.com wrote: | On 31 May 2008 10:45:59 GMT, snipped-for-privacy@ipal.net wrote: | |>So what would you use for a group of computers that need to be connected to |>power from a single outlet for maximum protection, which use more than the |>current allowed on a 5-15P plug? | | 6-15 power cords and switch the PS to 240v

Power strips and point of use surge protectors for 240v circuits that are 120v relative to ground are definitely hard to find and may not even exist. Do you know of any?

I have seen a power strip / surge protector with L5-20P plug and 5-15R outlets.

On Sat, 31 May 2008 23:44:50 -0400 Michael A. Terrell wrote: | snipped-for-privacy@aol.com wrote: |> |> On 31 May 2008 10:45:59 GMT, snipped-for-privacy@ipal.net wrote: |> |> >So what would you use for a group of computers that need to be connected to |> >power from a single outlet for maximum protection, which use more than the |> >current allowed on a 5-15P plug? |> |> 6-15 power cords and switch the PS to 240v | | | | Or multiple 120 VAC circuits, like we do in broadcast studios and | CATV headends.

I want common surge protection on the metallically interconnected computers. So it all needs to come off a single outlet and go through a single surge protector. Also, since the build is not metallically shielded and hence will not provide added protection against induced surges, common surge protection needs to be as close to the equipment as possible to minimize the lengths of conductors after the final surge protection.