wire sizing

[Ivan Young]

Thanks for your reply textie. So I guess what you are saying is that my friend should install a ground rod. Should he separate the grounding wires from the neutrals by putting them on their own grounding bar? Also how would he find the open neutral?

 

[texie]

Thanks for your reply textie. So I guess what you are saying is that my friend should install a ground rod. Should he separate the grounding wires from the neutrals by putting them on their own grounding bar? Also how would he find the open neutral?

No, in this case you can't isolate the neutrals from the grounds as that would create a new, serious, hazard by removing the fault return path. Can't site the NEC reference off the top of my head as to the relevent Art 250 items to make this compliant. The open/weak you just use basic trouble shooting skills. Better find it quick, as if there are any sensitive loads you are likely to lose them. Draw a 120/240 circuit out and see if you can figure out why this can do so much damage if not repaired ASAP.

 

[Ivan Young]

Thanks again Texie. I did a little research and I came up with this. If a EGC was not installed from main panel to the sub-panel then you have to reground the neutral at the second panel .Either way a grounding electrode is required at the second building and a GEC is ran between the grounding bus and the electrode. You can also run a EGC from the main panel to the sub-panel and keep the neutral bus isolated from the sub-panel and the grounding bus. How am I doing so far?

 

[texie]

Thanks again Texie. I did a little research and I came up with this. If a EGC was not installed from main panel to the sub-panel then you have to reground the neutral at the second panel .Either way a grounding electrode is required at the second building and a GEC is ran between the grounding bus and the electrode. You can also run a EGC from the main panel to the sub-panel and keep the neutral bus isolated from the sub-panel and the grounding bus. How am I doing so far?

You're on track now.

 

[kwired]

Thanks again Texie. I did a little research and I came up with this. If a EGC was not installed from main panel to the sub-panel then you have to reground the neutral at the second panel .Either way a grounding electrode is required at the second building and a GEC is ran between the grounding bus and the electrode. You can also run a EGC from the main panel to the sub-panel and keep the neutral bus isolated from the sub-panel and the grounding bus. How am I doing so far?

You are correct.

In the situation you describe there is still an open neutral someplace and installing a grounding electrode will not solve the problem. If the electrode is metal water piping that is connected to electrical system in another structure it can mask the problem as the water piping will ultimately become the primary path for neutral current.

 

[Ivan Young]

Thanks Texie and Kwired, I understand that a grounding electrode must be installed regardless but that would not solve the problem that exists. The open or partially opened beutral must be found and fixed. So I will pass the info to my co-worker and see what happens. Many thanks for all the help.

 

[Ivan Young]

Hello gentlemen, I have another question. When installing a disconnect what determines if you install a fused or non-fused disconnect?

 

[kwired]

Hello gentlemen, I have another question. When installing a disconnect what determines if you install a fused or non-fused disconnect?

First thing - I think since you are asking a new question on a new topic you should probably start a new thread, since you started this thread it is kind of yours anyway but still not a bad idea.

In answer to the new question - overcurrent devices are not always necessary. Depends on the reason for the disconnect. If there is already sufficient overcurrent protection for the application and all that is needed is a disconnecting means then an unfused disconnect is certainly acceptable - does not necesarily mean anything is wrong with providing a fused disconnect.

If required overcurrent protection is not already provided for what is being served lets say a tap from a feeder then you must have overcurrent protection - the conductors on the load side of your disconnect are not properly protected by the overcurrent device supplying the feeder.

You generally need disconnecting means if you also need overcurrent protection devices.

 

[Ivan Young]

Thanks Kwired, we have a 480v 3ph dust collector with a 30amp breaker protecting it from the panel. Management decided that a disconnect wa s needed within site of the equipment.

 

[kwired]

Thanks Kwired, we have a 480v 3ph dust collector with a 30amp breaker protecting it from the panel. Management decided that a disconnect wa s needed within site of the equipment.

If that 30 amp breaker provides the necessary overcurrent protection you can put however many other switches in the circuit you desire (rated for the load of course) and no additional overcurrent protection is required.

 

[tom baker]

Ask your foreman what the ampacity of a 12 THHW conductor is.
Its not 20 amps, by the way.
And realize that there is difference between overcurrent and conductor ampacity, take a look a table 310.16 or what is now 310.15(B)(16) and the **note

 

[Ivan Young]

Thanks guys for your help

 

[Strife]

Thanks for all the replies guys. I take it the way the calculations were done correctly.
The reason a counted the neutral for the dryer is because the light inside the drum is 120v, so is it ok to count it? I asked a forman on the job and he said the neutral should always be counted. I thought it is counted for receptacles, lighting, and when your load is unbalanced.
Thanks,
Ivan

Yeah, but the light only comes on when the door is opened, which in turn shuts down the heater. Besides the light in the dryer is the least of your worries
Manufacturers use the neutral to set different heating points.
For instance a 10KW at 240 doesn't use the neutral at all.
Same 10KW at 120V uses one phase and the neutral, BUT it's only 5KW now.
Now take 4 heaters and play with them all day long, you can achieve all kind of different levels of heat, but in NO WAY you'll get any combined amperage greater than that of 2 wires at their max.

 

[kwired]

Yeah, but the light only comes on when the door is opened, which in turn shuts down the heater. Besides the light in the dryer is the least of your worries
Manufacturers use the neutral to set different heating points.
For instance a 10KW at 240 doesn't use the neutral at all.
Same 10KW at 120V uses one phase and the neutral, BUT it's only 5KW now.
Now take 4 heaters and play with them all day long, you can achieve all kind of different levels of heat, but in NO WAY you'll get any combined amperage greater than that of 2 wires at their max.

If a resistance heating element is 10kW @ 240 volt you will only get about 2.5kW out of it if only 120 volts is applied.

The resistance does not change. Resistance is approximately 5.8Ω.
120V ? 5.8 Ω = 20.7A.
20.7A X 120V = 2484 VA = 2484 watts (rounding off has dropped the final result - if you don't round off to 1/10's you get even closer to 2500, resistance is actually 41-2/3 which is a never ending .6666...)

 

[Ivan Young]

Thanks for all the replies. I must point out that most domestic dryers even though it is 240v, the motor, timer, selector switch, and light is all 120v, it is only the heating coils in the case of a electric dryer that is 240v.

 

[kwired]

Thanks for all the replies. I must point out that most domestic dryers even though it is 240v, the motor, timer, selector switch, and light is all 120v, it is only the heating coils in the case of a electric dryer that is 240v.

Which to be technically correct the circuit is 120/240 volts three wires. Also referred to as a multiwire branch circuit.

They still work on 120/208 just with less heat output. Motor and other 120 volt controls still have 120 volts and don't know any difference.

 

[Ivan Young]

Then in this case the neutral must be counted as a current carrying wire?

 

[Dennis Alwon]

Then in this case the neutral must be counted as a current carrying wire?

IMO, the neutral would be a CCC in this case.

 

[Ivan Young]

Thank you Dennis, thats what I thought

 

[Smart $]

Which to be technically correct the circuit is 120/240 volts three wires. Also referred to as a multiwire branch circuit.

They still work on 120/208 just with less heat output. Motor and other 120 volt controls still have 120 volts and don't know any difference.

Just o be technically correct, this circuit is only permitted to be [called] a multiwire branch circuit by exception. 210.4(C) general says a MWBC shall supply only Line-to-Neutral loads. The two exceptions thereto permits one utilization equipment or where ocpd opens all ungrounded simultaneously. A dryer circuit typically meets both exceptions' conditions.