Trouble with Compressor blowing Breaker

[BIGUN]

Inspector507, I am curious, what problem is being addressed and corrected by going from a 3-wire to a 4-wire dryer plug? Never realized my 3-wire plug was inadequate so I changed the receptacle at my new house from 4 to 3-wire to match my 3-prong dryer plug. What is the reason for the new grounding requirement? /forums/images/graemlins/confused.gif

 

[Inspector507]

The 3-wire cord/outlet combination essentially used the neutral to ground the dryer/range. The dryer/range need a neutral AND a ground. Thats why they changed to the new 4-wire set-up.

 

[fwc]

The theory behind having ground wires is they are protective and provide a safety path for a short to follow ( going thru the wire instead of <font color="red"> YOU </font> hopefully) and then kick the breaker. Protective Ground wires are not supposed to be the same as the neutral in that they never carry any current unless there is a fault. I suspect that 3 wire 220 circuits got away with it because in a well balanced 220 circuits, the neutral didn't really carry much current because each 110 Volt leg is 180 degrees out of phase with each other and if the load is balanced between each 110 leg, the current in the common winding (neutral) would be zero. If not balanced, the current in the third wire (also the center tap of your local power transformer outside your house) is the current difference between load of the phases.

Well anyway... thats what I heard... /forums/images/graemlins/smile.gif

FWIW,

fwc

 

[BIGUN]

I guess with a pure 220-volt load, such as a compressor, there is no current flow through the neutral so it doesn’t need one, only a ground. With a dryer, you have the interior light and the timer motor which are likely 110-volt and would require a neutral. If under normal operation any current at all flows through the neutral, you are required to have a separate ground I suppose.

 

[fwc]

I'm guessing that they want the protective ground to be able to shunt the entire current supplied to the load to ground until the breaker opens. Having a separate ground wire available means there will never be any current flow in it so its probably safer - I suspect the newer code requirements would require it - but have not looked. It may depend on the type of load also - If someone gets really bored.. the NEC is probably on the web somewhere.. /forums/images/graemlins/smile.gif


fwc

 

[Junkman]

Inspector.... Please read this article and comment...... thanks Junkman..... incorrect dryer instructions from manufacturer

 

[Inspector507]

The appliance manufacturers info was indeed incorrect and I would assume since that info is 7 years old by now, they have corrected the situation.
Exactly which part were you wanting comments on? /forums/images/graemlins/confused.gif

 

[Junkman]

the use of the ground rod...... I realized after posting that the information is old, but I find it interesting that there has been no updates to this information. what is the correct use and placement of the ground rods.... could you please post a line drawing like the other one, showing how a drier is wired using 4 wires...... thanks for your information and help......

 

[Inspector507]

The ground rod is NEVER to be used as the grounding means for any appliance.

The attached diagram is how a 4-wire cord is to be hooked up. Soemtimes there is a ground strap connected to the center terminal and goes to the dryer cabinet. That has to be removed to use the 4-wire cord.

Green goes to the cabinet
Black to one of the outside posts/terminals
Red to the other outside post/terminal
White(neutral) to the center one

 

[Bird]

</font><font color="blue" class="small">( Soemtimes there is a ground strap connected to the center terminal and goes to the dryer cabinet. That has to be removed to use the 4-wire cord )</font>

My youngest daughter just bought a new dryer; been using an old one that was given to her by a neighbor. That neighbor had been using a 3 wire plug and changed to put the 4 wire plug on it when he installed it for her. When I pulled it out to install the new dryer, I found that the old one had that ground strap, and instead of removing it, he had just hooked both the white and green wires to that center terminal. /forums/images/graemlins/laugh.gif