T-slot plugs and 20 amp appliances?

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.
Bill

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

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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.

On Fri, 30 May 2008 12:47:40 +0000 (UTC) Michael Moroney
| |>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 31 May 2008 10:45:59 GMT, snipped-for-privacy@ipal.net wrote:
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6-15 power cords and switch the PS to 240v

snipped-for-privacy@aol.com wrote:
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Or multiple 120 VAC circuits, like we do in broadcast studios and CATV headends.

On Sat, 31 May 2008 23:44:50 -0400 Michael A. Terrell
| snipped-for-privacy@aol.com 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.

snipped-for-privacy@ipal.net wrote:
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Not if using shunt protectors. The equipment must be on the same circuit, but can be fed through multiple receptacles, and you can install multiple shunt type protectors. A single point of use protector is often impractical/impossible for multiple pieces of equipment. That may not be an ideal situation, but it is nonetheless a common occurence.
Ed
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ehsjr wrote:
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Multiple circuits also prevent the complete shutdown of all the servers if there is an electrical fault in a server room. Some headends had six 120 V, 20 A circuits for the electronics, and a 240 V, 20 A circuit for the room's air conditioner.

On Sun, 01 Jun 2008 23:02:14 -0400 Michael A. Terrell
| | ehsjr wrote: |>
|> > On Sat, 31 May 2008 23:44:50 -0400 Michael A. Terrell
|> > |>
|> > |> |> > |> >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. |> |> Not if using shunt protectors. The equipment must be on the |> same circuit, but can be fed through multiple receptacles, and |> you can install multiple shunt type protectors. A single |> point of use protector is often impractical/impossible for |> multiple pieces of equipment. That may not be an ideal |> situation, but it is nonetheless a common occurence. | | | Multiple circuits also prevent the complete shutdown of all the | servers if there is an electrical fault in a server room. Some headends | had six 120 V, 20 A circuits for the electronics, and a 240 V, 20 A | circuit for the room's air conditioner.
Where things go to the extreme that multiple circuits cannot be avoided then you have to deal with that. But where the scale is still small enough to be done with a single circuit, then it should be.
This is for a home server room. It's not mission critical. If a 20A or 30A 240V or 120/240V circuit is sufficient, then why not. Keep in mind that all PCs these days are fully able to operate directly from 240V. Lots of wall warts can be had that will as well (though in many cases you may have to get the Europe versions). What little remains that still needs 120V can be fed through a small stepdown transformer.

On Sun, 01 Jun 2008 17:24:43 GMT ehsjr
| Not if using shunt protectors. The equipment must be on the | same circuit, but can be fed through multiple receptacles, and | you can install multiple shunt type protectors. A single | point of use protector is often impractical/impossible for | multiple pieces of equipment. That may not be an ideal | situation, but it is nonetheless a common occurence.
Where the supply wires break apart determines the degree of induced difference voltage. The closer to the equipment this is, the less the difference. And the use of a common protector closer to the equipment helps ensure a minimum difference.
It's a matter of degree. And I want it all.

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.

snipped-for-privacy@ipal.net writes:
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I have seen a commercial/industrial power strip that had a few 6-15R duplex recepticles, at the same company where I got the workbench. No good for 120V devices since 6-15R recepticles have no neutral. I don't remember what sort of plug its cord had.
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A regular consumer-grade power strip (not the one in my workbench) rated for 20A and a regular 5-20P would be useful for people with larger setups. They probably don't exist for residential service simply because many people would buy them by mistake not seeing/knowing about the plug, and either return it or replace the plug and overload a 15A circuit, and relatively few will wind up being used properly.
The fact all consumer-grade power strips have a switch and a 15A breaker tells me that regulations somehow consider them different from "extension cords" which can also easily be overloaded even if all devices plugged into them use less than the rated current of a 5-15P plug.

On Mon, 2 Jun 2008 15:30:57 +0000 (UTC) Michael Moroney
| snipped-for-privacy@ipal.net writes: |
|>| |>|>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 commercial/industrial power strip that had a few 6-15R | duplex recepticles, at the same company where I got the workbench. | No good for 120V devices since 6-15R recepticles have no neutral. I | don't remember what sort of plug its cord had.
If I had one of those, it would just be run at 240V and the lack of neutral would not be a problem.
|>I have seen a power strip / surge protector with L5-20P plug and 5-15R outlets. | | A regular consumer-grade power strip (not the one in my workbench) rated | for 20A and a regular 5-20P would be useful for people with larger setups. | They probably don't exist for residential service simply because many | people would buy them by mistake not seeing/knowing about the plug, and | either return it or replace the plug and overload a 15A circuit, and | relatively few will wind up being used properly.
If they have a power demand that exceeds a 15A circuit, putting it all on a 15A circuit is a bad thing regardless of whether the power strip is the right type or not. Still, it can make for less safe usage when people cut off the plug and insert their own.
I have seen a 5-20P -> multiple 5-15R strip. It was presumably intended for the larger cases of usage. Maybe they also make a 5-20P -> multiple 5-20R or even 5-20P -> multiple 5-20RALT.
But what I want is the 6-15P or 6-20P strip that has 6-15R or 6-20R outlets. I'd rather have that over the readily available Schuko strips because the surge protection within could be correct with respect to the voltage clamp level for the conductor to ground MOVs (needs to be based on 120V supply as in North America rather the 230V supply as in Europe).
| The fact all consumer-grade power strips have a switch and a 15A breaker | tells me that regulations somehow consider them different from "extension | cords" which can also easily be overloaded even if all devices plugged | into them use less than the rated current of a 5-15P plug.
I still occaisionally see some that do not have the switch/breaker.
I will need to investigate the usability of the "whole house" panel protectors (the kind that plug into 2 or 4 breaker panel slots) for computer rack.

snipped-for-privacy@ipal.net writes:
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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.

wrote:
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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: http://phil.ipal.org/usenet/aee/2008-05-28/ks-3.html
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.

<SNIP>
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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
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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.

| "Jeff Strickland" wrote |> |> "Stephen B." wrote in message
|>> |>> <SNIP> |>>> |>>> 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.