poweringtech
Member
What is the voltage limit for High Resistance Grounding? Will the code allow High Resistance Grounding for 240Y or 460Y voltage system?
poweringtech said:If...ungrounded system can be used for 240 volts...
Yep, there are a bunch. I'm not one, cause I know I don't understand what the code panels think they are saving us from.poweringtech said:Any expert here on system grounding?
I'v never seen 240Y. Did you mean 208Y? If you did, as has already been said, it would have to be grounded (250.20B1)poweringtech said:...Will the code allow High Resistance Grounding for 240Y ...
I have no idea - and I've looked plenty.poweringtech said:...How will it be unsafe if HRG is applied to lower than 480 volts?...
George - 240 is always Delta. There is no way to ground it and have the ungrounded conductors 150V or less. (Possible oddball exceptions noted.) So, 240D is exempt from 250.20B1. Now if it were 240/120D, then 250.20B3 would apply, and it would have to be grounded.GeorgeS said:...Originally Posted by poweringtech: ...ungrounded system can be used for 240 volts...
I don't believe that to be correct, according to 250.20(B)(1), but am not certain of that....
And for 1000V and up see 250.186GeorgeS said:...Impedance Grounded Systems are permitted for voltages between 480V and 1000V. See 250.36....
Pretty well asked and answered. Personally, I really don't know.poweringtech said:...Why will the code allow ungrounded for 50 volts to 1000 volts while limit HRG to 480 to 1000 volts. Isn't it that HRG is safer than Ungrounded system based on IEEE 142-1991?....
The typical configuration is midpoint grounded, which puts the L-N voltage (the voltage referenced in 250.20(B)(1)) at 120V.coulter said:George - 240 is always Delta. There is no way to ground it and have the ungrounded conductors 150V or less.
georgestolz said:The typical configuration is midpoint grounded, which puts the L-N voltage (the voltage referenced in 250.20(B)(1)) at 120V.
Edit: Actually, it looks (on further review) as though (B)(1) is intended for single phase, (B)(2) for 120/208 three phase, and (B)(3) for 120/240 midpoint grounded delta three phase. Agreed, Carl?
That's true. I believe I have even seen transformers cataloged with that connection. I've never seen one in use. What do you think would be the design drivers behind specifying this?poweringtech said:... designer in the future may insist on 240Y/139 volts system using 240 volts 3 phase and 240 volts single phase line-to-line. ...
I've seen pictures of this in books as well, but again, never seen one installed. Again, why?poweringtech said:....DELTA may converted to a HRG by installing a grounding tranformer or zigzag transformer and connecting a resistor to convert them to HRG.
coulter said:That's true. I believe I have even seen transformers cataloged with that connection. I've never seen one in use. What do you think would be the design drivers behind specifying this?
carl
Or, order a 240D/480Y DIT (or 460Y).jim dungar said:...If your service was 240V 3PH and you wanted a DIT then you would need a 240Y unit. ...
I'd easily agree with the second half of that.jim dungar said:...If your equipment came from overseas it might be rated for 240V only (why people don't specify voltage when they order special equipment is beyond me)....
Having worked in a papermill, I wouldn't find that odd at all.jim dungar said:...I have just finished some systems studies at three different paper mills and they all had a mix of 480Y and 240Y DITs.
brian john said:In the Maryland suburbs outside of Washington DC the standard voltage is 460 as supplied by the utility