Electrical wiring

[Bert the Weldor]

Now that I have my motor and VFD, I have to wire it up. Problem is the wiring kit that came with it has a Nema 6-30p plug and I'd like to plug the grinder into one of my Nema 6-50r receptacles. Now, not knowing a lot about electrical, I know that that creates an problem in that the breaker won't trip until 20+ amps over the wire/motor limit. But, if it's just me in the shop using the grinder, could I get away with putting a Nema 6-50p on the motor power cord and be good. OR... make an adapter. Any electricians out there give me some suggestions?
Thanks guys!!

 

[Dabbler]

There is no problem plugging a 30 amp appliance into a 50 amp plug with the proper plug.

 

[Bert the Weldor]

Thanks Dabbler. So I guess by that means a short adapter cord would be fine too.
So what is the risk in doing this? Just so I know what to look for. Bert's Law being what it is.

 

[RobinHood]

So what is the risk in doing this? Just so I know what to look for.

Bert, here is what I would do: Trace the 50A welder circuit in question back to the breaker box and locate the 50A breaker. I would then replace it with a 30A breaker. At the other end, I would replace the existing 50A wall welding receptacle with a correct NEMA 6-30R one. Plug in your grinder into this dedicated "30A Grinder Circuit". You will never overload any of the wire leading from your panel to the grinder because it is rated for 50A. Yet, you limit the amount of current that can reach the grinder to 30A by the new, lower power, breaker. You have basically "de-rated" the existing circuit.

Anyone share this opinion?

 

[Dabbler]

-- Just like there's a 18ga lamp cord to a unprotected lamp on a 15 A circuit, down-rating a plug to a lower value appliance is just fine. If the lamp shorts out, it can be a problem, of course. That how things are done in North America... In Europe, there is significantly more protection for any given appliance. Your welder will have other protections built in, and should not present any risk at all.

 

[Bert the Weldor]

Thanks Robin. I had thought of that but stopped short as that would take one of two 50amp circuits. I have four in the shop. Two on one 50 breaker and two on another, thus able to run two welders at a time. (my friend comes to my shop on weekends sometimes). However, it could be sacrificed if needed, so still a good idea. Thanks.

Dabbler: It's that shorting out that I worry about and I'm sure my insurance agent would have something to say about it to. Ha ha.

Just for the sake of spit balling ideas: I guess one could make a sub box w/ a 30amp breaker that plugs into the welder receptacle and has a Nema 6-30 female receptacle extension cord on the other side. Basically down rating the 50amp circuit.
Or just run a surface conduit from the main box to Nema 6-30 receptacle and be done with it.

 

[RobinHood]

Just for the sake of spit balling ideas: I guess one could make a sub box w/ a 30amp breaker that plugs into the welder receptacle and has a Nema 6-30 female receptacle extension cord on the other side. Basically down rating the 50amp circuit.
Or just run a surface conduit from the main box to Nema 6-30 receptacle and be done with it.

Both would work fine and protect your grinder from a potentially massive 50A.

 

[alman]

Hi all, , IMHO, most devices nowadays have their own circuit breaker for protection in the housing, therefore, leaving the 50A breaker in the panel is fine, using the same crowfoot plug / receptacle is also fine, , , if the device DOES NOT have its own breaker / fuse in it, just don't overload it, , easy-peasy

 

[kylemp]

The general idea behind the breakers in your panel is they are gauged to the wire running into them. What you plug in becomes your problem, it's not accounted for in the electrical code as far as I know. Anything plugged in is supposed to be certified by a testing body to make sure it has its own safety mechanisms.
I agree with @RobinHood that running a 30a breaker and plug would be a better idea but you could just throw a 50a plug on it knowing you're the one who is using it and not leaving it plugged in. Personally I kill all the breakers to my tools when I'm walking out the door just so I don't have to worry about anything going wrong and I run 50a plugs on everything regardless of the tool power requirements.

 

[alman]

The general idea behind the breakers in your panel is they are gauged to the wire running into them. What you plug in becomes your problem, it's not accounted for in the electrical code as far as I know. Anything plugged in is supposed to be certified by a testing body to make sure it has its own safety mechanisms.
I agree with @RobinHood that running a 30a breaker and plug would be a better idea but you could just throw a 50a plug on it knowing you're the one who is using it and not leaving it plugged in. Personally I kill all the breakers to my tools when I'm walking out the door just so I don't have to worry about anything going wrong and I run 50a plugs on everything regardless of the tool power requirements.

my mother would uplug stove an dryer before she left the house, , , the breakers are a 'means of protection for circuit overload and short circuits', , , I leave everything on, as many breakers, over time and usage - flipping on-off will weaken with fatigue. jus sayin, , ,

 

[kylemp]

Mmm.. I'm not dealing with a factory built stove though. Breakers failing over time is a small concern to something I wired while I was tired and not really paying attention deciding to burn down my empire of dirt.

 

[Max Simons]

Hey guys,

I'm an electrician by day and a hobby machinist by night. Breakers are sized to protect the size of conductor they are feeding. In this case, you're welder is most likely on a 40A breaker connected to #8AWG.

The only thing that could happen if you use that circuit for your grinder is that, if you overload the grinder, the flexible cord from the grinder could get hit and possibly melt. That being said, the grinder motor is most likely a split phase type and will drop out if you load it up too much. (If you slow it down below 75% of rated speed, the internal centrifugal switch will close and you will have to wait for it to speed back up)

 

[Bert the Weldor]

Hey guys,

I'm an electrician by day and a hobby machinist by night. Breakers are sized to protect the size of conductor they are feeding. In this case, you're welder is most likely on a 40A breaker connected to #8AWG.

The only thing that could happen if you use that circuit for your grinder is that, if you overload the grinder, the flexible cord from the grinder could get hit and possibly melt. That being said, the grinder motor is most likely a split phase type and will drop out if you load it up too much. (If you slow it down below 75% of rated speed, the internal centrifugal switch will close and you will have to wait for it to speed back up)

Thanks Max. The breaker is a 50a. Got a ton of room on my 200 amp panel so going to look at putting in a separate breaker. If not doable, then I'll wire a 50a male to the grinder and just pay attention to it. I'm a one man shop so no shop monkeys to worry about.
Now, if I could just get time to finish putting the darn thing together!!
Thanks for the help!