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#198713  02/02/11 02:27 AM
Ampacity

New Member

Joined: Feb 2011
Posts: 2
Canada


im in school right now got a few questions from the CEC.
Minimum size of NMD90 for hot water tank 4500 watts 240v?
Minimum size of Dryer NMD90 for dryer 6000w 240v?
Can you explain to me how to calcuate using the code book? thanks



#198736  02/02/11 07:55 PM
Re: Ampacity
[Re: Deakn]


Answer 1 = #10 4500/240*1.25 = 23.44 amps. next wire size is 10
second answer same math =31.25 amps so next wire size is #8.
Ok so here is a trick question residential range 12,000 watts at 240 volts. I'll give you the answer you tell me why. 8000/240 = 33.33 or #8 Hint answer is in section 8



#198739  02/02/11 09:29 PM
Re: Ampacity
[Re: Deakn]

New Member

Joined: Feb 2011
Posts: 2
Canada


Why do you multiply by 1.25? which rule is that



#198746  02/02/11 11:19 PM
Re: Ampacity
[Re: Deakn]


In NEC if a load is continuous you must use wire size and overcurrent protection rated for 125% of the nameplate rated ampacity. If I recall a continuous load is one that will be in use for 3 or more hours consecutivly.
Jimmy
Life is tough, Life is tougher when you are stupid



#198885  02/07/11 01:26 AM
Re: Ampacity
[Re: Deakn]


A continuous load, under 225 amps, is a total of 1 hour in any two hour period, under normal operation. If you normally operate your drier at high heat for more than one hour at a time, it might be continuous. Unless you have a commercial dryer, the element will cycle, and it probably isn't continuous. In my home, the dryer runs for a few hours on the weekend, so the normal operation is off. Since I can select "any two hour period", I'll pick a weekday. It clearly doesn't say "every" two hour period.



#199940  03/14/11 10:37 PM
Re: Ampacity
[Re: Deakn]


Let me answer
First 12 kw at 6000w over 12 kw @ 40% why did you say 8000/240 am I wrong...I don't have code home but I will deffinetly check tomorow
Other loads over 1500 w are taken at 25%: Dryer 4 kw@25% 1000 w
“If you don't know where you are going, any road will get you there”.



#199984  03/16/11 02:44 PM
Re: Ampacity
[Re: Deakn]


A 12 KW range in domestic use is considered to have a 8000 watt demand see 8300. This is why we use 83 instead of 63 to feed a 12 kw range 8kw=33.33 amps on a 40 amp breaker 12 kw = 50 amps and in a commercial application X 1.25 or 62.5 amps on an 70 amp breaker The range itself is different too. A domestic range while capeable of using the full 12 kw with all 4 elements and both oven elements on high it does so for ver brief periods. Domestic ranges are not approved for use in a restaurant even though they often try to use them since they are 1/4 the cost.
The commercial range is rated for use the whole day, every day.




