[Thisiseasy]

I'm replacing a dryer at one of my properties. The dryer outlet is three blade and the dryer cord is four blade.

Since its a metal box connected with conduit can't I just replace the three blade outlet with a four blade outlet? The box is ground right? I tested and get 118V from each leg to the box with the multimeter.

 

[rjniles]

No, the circuit must be 4 wire, use complete metal conduit or Type AC or MC cable. Unless you are sure you have a valid ground the safest option is install a 3 wire cord on the dryer.

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[seharper]

I'm replacing a dryer at one of my properties. The dryer outlet is three blade and the dryer cord is four blade.

Since its a metal box connected with conduit can't I just replace the three blade outlet with a four blade outlet? The box is ground right? I tested and get 118V from each leg to the box with the multimeter.

blink blink did that just happen? Someone ran into the 3-prong/4-prong issue and their very first thought was to go for the much safer 4-prong connector instead of the obsolete and dangerous (but universal) 3-prong?

Congrats. I think that's the first time I've seen that.

Yes, that's exactly the right thing to do.


OP, I'm assuming you are talking about metal conduit here. If the conduit is non-metal, or certain types of flexible, then no, you need a ground wire. Fortunately there are generous retrofit rules that do not require the ground wire to be in the pipe (but that is probably the easiest).

No, the circuit must be 4 wire, use complete metal conduit or Type AC or MC cable.

Metal non-flex conduit is a perfectly valid ground path. No ground *wire* need be used and a 3-wire (hot hot neutral) connection to a NEMA 14-30 is exactly correct.

You can add a ground wire if you really want to... I've been known to do it as a "belt and suspenders" measure where I thought the EMT had a chance of getting wacked or rusting out. But it's not required.

Use of the shell of flexible metal conduit is hit-and-miss - I don't remember the gory details - but it depends on cable type and application.

Unless you are sure you have a valid ground the safest option is install a 3 wire cord on the dryer.

The words "safest" and "3-wire cord" do not belong in the same sentence!

3-wire installations are scary dangerous. A trivial problem - a loose neutral wire - will, with certainty, electrify the chassis of the dryer. If the operator touches the dryer chassis and anything that is grounded - gosh, water pipes, nearby sink, how about the washing machine 1" away - kablammo. This flaw has a body count.

 

[chetwisner]

Do 14-50s and 6-50s have the same straight blade configurations? From what I'm looking at, the slots are different in sizes.

 

[chetwisner]

Also, I don't recall if a dryer has a strap that needs to be bonded to the neutral if using a 3-wire (6-50).

 

[afjes2015]

No they will not have the same blade configurations for the safety fact that one plug can not go into a receptacle that does not match volts and amperage ratings.


Here is a chart to help you understand. Take a look at it.


Also most electric dryers are 30amp not 50amp.

 

[afjes2015]

No they will not have the same blade configurations for the safety fact that one plug can not go into a receptacle that does not match volts and amperage ratings.


Here is a chart to help you understand. Take a look at it.


Also dryers are usually 30amp not 50amp

 

[Jim Port]

Flexible metallic conduit can only be a ground for circuits rated 20 amps or less and only if 6 foot or less.

 

[seharper]

No they will not have the same blade configurations for the safety fact that one plug can not go into a receptacle that does not match volts and amperage ratings.

Well, actually, it *would* make sense for a NEMA 6-30 to plug into a 14-30.... and for a 6-50 to plug into a 14-50. There's no trouble with that. But unfortunately they had not done that. I suspect NEMA 6 came along before NEMA 14, and there simply wasn't room to squeeze a neutral onto the 6.


However, it's just as easy to remove the 6-50 plug and fit a 14-50 plug (and just don't use the neutral). And this is one case where a cheater cord is reasonable and legal (or at least UL-approve*able*).

 

[Thisiseasy]

OP, I'm assuming you are talking about metal conduit here. If the conduit is non-metal, or certain types of flexible, then no, you need a ground wire. Fortunately there are generous retrofit rules that do not require the ground wire to be in the pipe (but that is probably the easiest).

I'm trying to attach a photo. This is of a switch in my basement, but this is the exact same type of box and conduit I'm referencing.

 

[seharper]

Yeah, that's EMT metal conduit. I have miles of that stuff in 4 buildings, and not a ground wire anywhere to be found. That's just fine.