Electrical: NEMA 10-50R

[astronomical]

My dryer is hooked up to this type of outles (50A 10-50R). Is it safe if I'm always running at 240V? Will the neutral always act as a ground when operating a 5500w element (at 240v). Also, what would be the most cost effective pigtail to make? I'm also open to the idea of putting a new plug in but id rather not have to run new line. This is all to try and hook up an MK5500. Thanks in advance

Astro

[Coaster]

@ astronomical,

Back ground concerning your NEMA 50A 10-50R receptacle ->

NEMA (U.S. National Electrical Manufacturers Association) 10-50R, 3-pole, 3-wire, non-grounding, 50A 120/240V. For older ranges that are non-grounded and that require dual voltage: 240V for the heating elements and 120V for lighting/clock/controls.

In North America, the cases of some ovens and clothes dryers were grounded through their neutral wires as a measure to conserve copper from copper cables during the Second World War. This practice was removed from the NEC in the 1996 edition, but existing installations may still allow the case of such appliances to be connected to the neutral conductor for grounding. Note that the NEC may be amended by local regulations in each state and city. This practice arose from the three-wire system used to supply both 120 volt and 240-volt loads. Because ovens and dryers have components that use both 120 and 240 volts there is often some current on the neutral wire. This differs from the protective grounding wire, which only carries current under fault conditions. Using the neutral conductor for grounding the equipment enclosure was considered safe since the devices were permanently wired to the supply and so the neutral was unlikely to be broken without also breaking both supply conductors. Also, the unbalanced current due to lamps and small motors in the appliance was small compared to the rating of the conductors and therefore unlikely to cause a large voltage drop in the neutral conductor.

Using the W (white wire) in NEMA 50A 10-50R receptacle as a ground should not cause any problem.

Regards,
Coaster

[astronomical]

Thanks coaster
FTR, the white wire is the one passing through the amp meter.. Thats the one I run to the neutral/"ground"?

heres what im thinking... Two sets of these http://www.ebay.com/itm/LEVITON-2621-AN ... 35b716e434" onclick="window.open(this.href);return false;" rel="nofollow (go off the picture.. i know its only for the plug).. Ill also pick up 10' of Sjoow 10/3 wire and a 10-50 plug for the outlet... Can I wire it like that?

50A outlet>50Aplug>30Aconnector>30Aplug>controller>30Aplug>30Aconnector> 5500Welement

Am I crazy? sorry for all the questions.. This stuff is foreign to me. Thanfully I didnt build the controller (thanks MK)

[KY1792]

FTR, the white wire is the one passing through the amp meter.. That's the one I run to the neutral/"ground"?

NO!

If you are talking about one of the SJO cord wires feeding the MK5500 then it should be connected to one of the Hot wires of the plug either X or Y on the 10-50R, the W on that receptacle is only for 120 volt use only. If the cord has black, white, green - hook black to X white to Y and green to W.

The 10-50R is exactly what Coaster has described and is known as a Hot-Hot-Neutral with no equipment ground, the L6-30P you linked to on ebay is a Hot-Hot-Ground, so is the SJO cable you mentioned. I would have no problem using it as you outlined but just be forewarned that you can not re-provision the green ground wire in that cord to be a neutral and be code compliant.

Not that it would matter for your "special purpose" just as long as you don't plug something into that twist lock that actually needed to be H-H-G fed from an isolated ground sub panel or loops can occur.

So in a nutshell hook the the black and white wires from the MK5500 to the straight "curved" blades of the ebay twist lock (should be brass and silver screws, hook the green wire to the keyed (L) blade or green screw. The white wire on the MK5500 is actually a hot and not a neutral - mark it with a wrap of black tape to ease your mind. The black and white from the MK should ultimately land on the two slanted prongs of the existing 50 amp receptacle.

[astronomical]

Thx KY.. I take it that in this scenario it won't matter that 10-50R is 3 prong and L6-30 is two prong.

[KY1792]

both are 3 prong, they are either HHN or HHG