Branch Circuit
- Thread starter Flight987
- Start date
- Status
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
210.19 and 210.20.
Branch Circuit
Is there somthing in the 2005 code that stated 80 Percent? Or how do I get the wording to tell me what it is?
I don't know why 80 Percent stay's in my head. 100 percent/ 125 percent=80 or 80 percent. Is that right?
My mind is playing trick's on me.
Is there somthing in the 2005 code that stated 80 Percent? Or how do I get the wording to tell me what it is?
I don't know why 80 Percent stay's in my head. 100 percent/ 125 percent=80 or 80 percent. Is that right?
My mind is playing trick's on me.
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
125% is 80% It depends on how you look at it. 80% of 20 amps is 16 amps or 125% of 16 amps is 20 amps. So the load cannot be greater than 125% of the 20 amp circuit means the same as 80% of the circuit capacity.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
80% is not there but it is the same as I explained above. Most people use 80% of the circuit as it is easier than 125% of the load,
Branch Circuit
Ques. How many Amps. of non-Cont. load may be added to a 30 Amp. branch circuit, which already supplies 11
Amps. of Cont. load? Key Answ. 16,
30x.80=24, 24-11=13 or is it
30-11=19, then 19x.80=15.2. Why is this so wierd. We are thinking that the 11 are allready have 1.25 in there.
It to simple to get wrong.
Ques. How many Amps. of non-Cont. load may be added to a 30 Amp. branch circuit, which already supplies 11
Amps. of Cont. load? Key Answ. 16,
30x.80=24, 24-11=13 or is it
30-11=19, then 19x.80=15.2. Why is this so wierd. We are thinking that the 11 are allready have 1.25 in there.
It to simple to get wrong.
How does one determine the correct wire size in the first place? As one of the others indicated it is based upon 125% of the continuous load +100% of the non-continuous load, then the breaker is selected to protect the wire base upon the wire's ampacity.
I one sticks to that you don't have to figure it backwards.
On a practical note it should be common knowledge that an existing circuit can not be loaded more than 80% of its ampacity. The common breaker is considered to be 80% rated or it can only be applied at 80% of its rating. But when originally selecting the wire sized based upon the 125%and100% rule and then selecting the breaker based upon protecting the wire it isn?t magic as the breaker of applied at 80% of its rating. As such don?t blame the breaker as being only 80% rated as it is the result of sizing the wire based upon the wire ampacity as related to 60/75degC or 75degC insulation.
The only time that a breaker can be rated at a 100% is if it is listed and applied per the instructions where the wire is sizes based upon 100%+100%, using 90degC rated wire sized per 75degC rated insulation protecting the "wire" with a 100% rated breaker.
Have you ever wondered why a common household vacuum has a maximum ampere rating of 12a? And check the amp ratings of other common household devices. 15a x.80 (80%) +12a.
Remember, it all starts with sizing the wire to carry the load and sizing the breaker to protect the wire base upon the wire size.
I one sticks to that you don't have to figure it backwards.
On a practical note it should be common knowledge that an existing circuit can not be loaded more than 80% of its ampacity. The common breaker is considered to be 80% rated or it can only be applied at 80% of its rating. But when originally selecting the wire sized based upon the 125%and100% rule and then selecting the breaker based upon protecting the wire it isn?t magic as the breaker of applied at 80% of its rating. As such don?t blame the breaker as being only 80% rated as it is the result of sizing the wire based upon the wire ampacity as related to 60/75degC or 75degC insulation.
The only time that a breaker can be rated at a 100% is if it is listed and applied per the instructions where the wire is sizes based upon 100%+100%, using 90degC rated wire sized per 75degC rated insulation protecting the "wire" with a 100% rated breaker.
Have you ever wondered why a common household vacuum has a maximum ampere rating of 12a? And check the amp ratings of other common household devices. 15a x.80 (80%) +12a.
Remember, it all starts with sizing the wire to carry the load and sizing the breaker to protect the wire base upon the wire size.
stickboy1375
Senior Member
- Location
- Litchfield, CT
UL and other testing laboratories list portable equipment (such as hair dryers) up to 100% of the circuit rating. The NEC is an installation standard, not a product standard, so it can't prohibit this practice. There really is no way to limit the load to 80% of the branch circuit rating if testing laboratories permit equipment to be listed for 100% of the circuit rating.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
I think your trying to apply the derating to the whole circuit instead of just applying it to the continuous load.
11 amps is your continuous load so we have to figure it separately:
11 + 25% = 13.75 this is the 125% figure we subtract from the circuit to know how much non-continuous load we can still apply to this circuit:
30 - 13.75 = 16.25
this is what it means in 210.19(A)(1):
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Curt-- Take the time to read the responses. Your question was answered. If you have 11 amps of continuous load then you calculate that at 125%. 11 times 1.25= 13.75 amps. A 30 amp cir can handle 30 amps of non continuous load. Now the load of a 30 amp circuit can handle 125% of the continuous load + 100% of the noncontinuous load. So 13.75 +16.25= 30 amps. So 16 amps is the answer
K8MHZ
Senior Member
- Occupation
- Electrician
I have seen hand held hair dryers that drew 18 amps and had a 15 amp plug. (Troubleshooting a 15 amp breaker that kept tripping....)
I just checked the one here and it is labeled as 1875 watts (15.625 amps). Actual testing showed 1480 watts drawing 13.2 amps.
Vacuums are getting much more efficient. My Hoover TurboPower 6000 uses less than 8 amps.
dkeaux@gmail.com
Member
- Location
- Greensburg, KY.~ USA
A 20 amp breaker loaded to 80% = 16amps a 16amp circuit at 125% is 20amps
stickboy1375
Senior Member
- Location
- Litchfield, CT
It probably drew 18 amps because nobody cleans them.
and a 15 amp breaker will never trip drawing 15.625 amps....
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
It probably drew 18 amps because nobody cleans them.
Why would that make it draw more?
stickboy1375
Senior Member
- Location
- Litchfield, CT
I guess I was thinking in terms of air restriction, not sure I'm correct now.
more load on the motor...I was going off my furnace motor, which monitors amperage and will increase speed as the filter gets dirty to self correct for proper air flow.
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