How are equipment ratings derived?

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mbrooke

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Ok- say you have a water heater, electric furnace, baseboard or even a restaurant grill. How is the current and/or wattage rating for those derived by the manufacturer? Is it the actual value at the listed voltage or a value multiplied by some number like 125% on AC units?



Reason I ask because while the NEC has us use the nominal voltage for our equations, in reality a circuit may be over 110% of the nominal voltage which will cause the equipment to draw more current than it label in theory.
 

Besoeker

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Ok- say you have a water heater, electric furnace, baseboard or even a restaurant grill. How is the current and/or wattage rating for those derived by the manufacturer?
By design for the most part I would think..........
 

Jraef

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Ok- say you have a water heater, electric furnace, baseboard or even a restaurant grill. How is the current and/or wattage rating for those derived by the manufacturer? Is it the actual value at the listed voltage or a value multiplied by some number like 125% on AC units?



Reason I ask because while the NEC has us use the nominal voltage for our equations, in reality a circuit may be over 110% of the nominal voltage which will cause the equipment to draw more current than it label in theory.
Typically a "rating" of a consuming device such as what you indicated is done by measurement at the stated utilization voltage, but with the understanding that per ANSI standards, utilization voltage can vary by +-10%. So for motors as an example, the NEMA MG-1 design specs state;
1.40 RATING OF A MACHINE
The rating of a machine shall consist of the output power together with any other characteristics, such
as speed, voltage, and current, assigned to it by the manufacturer.
Earlier in MG-1, they referenced ANSI C84.1-1989, Electric Power Systems and Equipment-Voltage Ratings (60 Hz), which is where the terms "Service Voltage" and "Utilization Voltage" are defined.
82589d1375406976-stepping-up-250v-440v-ansi_c84.1_voltage_tolerances.jpg
 

mbrooke

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UL rates residential appliances at least at the current they consume at 125 V, 60 Hz. For Ranges and such it is done at 250 V.

So technically, 110% of the nominal voltage is already considered.



For motors. I'd expect to see design V, kW, frequency, cos phi, rpm, etc....
For a heater, V and kW.
Not sure what you are asking.


Picture an electric shower rated 13 amps, 230 volts and 3000 watts. What are those 13 amps based upon? If they are based at 230 volts, then technically the wire size and MCB sizing would be incorrect in some scenarios since 230 volts is a nominal voltage. The supply could legally be 253 volts. As such, at 253 volts, the current draw will be 14.3 amps instead of the listed 13 amps- in theory.


Yes an electric shower or oven may cycle once the correct temp is reached- but consider a baseboard heater or storage water heater that may run for some length of time.
 

mbrooke

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Typically a "rating" of a consuming device such as what you indicated is done by measurement at the stated utilization voltage, but with the understanding that per ANSI standards, utilization voltage can vary by +-10%. So for motors as an example, the NEMA MG-1 design specs state;

Earlier in MG-1, they referenced ANSI C84.1-1989, Electric Power Systems and Equipment-Voltage Ratings (60 Hz), which is where the terms "Service Voltage" and "Utilization Voltage" are defined.
View attachment 20021


Ok- so then I could say 103.5 through 126.5 volts is taken into account for all equipment, and which ever yields the higher draw gets put on the rating tag?
 

JFletcher

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All of the equipment you listed are continual loads, there's already a 25% margin for them. Sure, a heater that uses 12 amps at 120 volts with number 14 wire and a 15 amp ocpd will be using 13 amps and put out 1560 Watts if run at 130 volts, which is too much for a continuous load on a 15 amp breaker. I believe the manufacturer's specifications are for nominal voltage, unless indicated otherwise, like you see on some hand held hair dryers, where the rated wattage is achieved at 125 or 130 volts so that they look more powerful than they are.

If I had a space or baseboard heater rated for 1440 Watts, and I knew my supply voltage was 130 volts, I would use number 12 wire on a 20 amp breaker.
 

mbrooke

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All of the equipment you listed are continual loads, there's already a 25% margin for them. Sure, a heater that uses 12 amps at 120 volts with number 14 wire and a 15 amp ocpd will be using 13 amps and put out 1560 Watts if run at 130 volts, which is too much for a continuous load on a 15 amp breaker. I believe the manufacturer's specifications are for nominal voltage, unless indicated otherwise, like you see on some hand held hair dryers, where the rated wattage is achieved at 125 or 130 volts so that they look more powerful than they are.

If I had a space or baseboard heater rated for 1440 Watts, and I knew my supply voltage was 130 volts, I would use number 12 wire on a 20 amp breaker.

Always continuous? What about restaurant equipment? What about the UK where continuous loads do not apply?
 

JFletcher

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Williamsburg, VA
Always continuous? What about restaurant equipment? What about the UK where continuous loads do not apply?

As I do not live in, do electrical work, or have any UK spec appliances, I cannot answer the question. Ask for the restaurant grill, okay you got me there.

What are you really asking here in this topic? As far as I know, all things are wired, and have ocpd based on nominal system voltages. The only exceptions I'm aware of are motors, which are rated/ labelled 230 / 460 volts, presumably to account for voltage drop on 240 and 480 volt systems.

Most manufacturers base their ratings from nominal system voltages. Some, who knows, like your average air compressor for home use listed at 5 horsepower, but only draws 10 amps on 120 volts. I believe those ratings may be based on Startup or locked rotor current.... or simply wishful thinking. Many portable home generators have similar peak power ratings that are advertised, however their continuous or steady-state wattages are much lower
 
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mbrooke

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As I do not live in, do electrical work, or have any UK spec appliances, I cannot answer the question. Ask for the restaurant grill, okay you got me there.

What are you really asking here in this topic? As far as I know, all things are wired, and have ocpd based on nominal system voltages. The only exceptions I'm aware of are motors, which are rated/ labelled 230 / 460 volts, presumably to account for voltage drop on 240 and 480 volt systems.

Most manufacturers base their ratings from nominal system voltages. Some, who knows, like your average air compressor for home use listed at 5 horsepower, but only draws 10 amps on 120 volts. I believe those ratings may be based on Startup or locked rotor current.... or simply wishful thinking. Many portable home generators have similar peak power ratings that are advertised, however their continuous or steady-state wattages are much lower


Take this for example:


s-l1600.jpg




32 amps at 208 volts single phase. Is 32 amps the current draw at 208 volts or 229 volts I guess I am asking.
 

Besoeker

Senior Member
Location
UK
Picture an electric shower rated 13 amps, 230 volts and 3000 watts. What are those 13 amps based upon? If they are based at 230 volts, then technically the wire size and MCB sizing would be incorrect in some scenarios since 230 volts is a nominal voltage. The supply could legally be 253 volts. As such, at 253 volts, the current draw will be 14.3 amps instead of the listed 13 amps- in theory.


Yes an electric shower or oven may cycle once the correct temp is reached- but consider a baseboard heater or storage water heater that may run for some length of time.
You'd probably wire in in 2.5mm^2
Adequate margin.
 

GoldDigger

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Take this for example:


s-l1600.jpg




32 amps at 208 volts single phase. Is 32 amps the current draw at 208 volts or 229 volts I guess I am asking.

I am quite confident that the current shown is for 208V, since no other voltage options are mentioned. I do not think that the high end voltage is taken into account. The range operates safely at 229V, but may draw more current. Which is fine since NEC is conservative and states the load calculations should use nominal voltage.

I would not try to operate it from 240 without consulting the manufacturer, as the heating elements would probably need to be changed.

Sent from my XT1585 using Tapatalk
 

mbrooke

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I am quite confident that the current shown is for 208V, since no other voltage options are mentioned. I do not think that the high end voltage is taken into account. The range operates safely at 229V, but may draw more current. Which is fine since NEC is conservative and states the load calculations should use nominal voltage.

I would not try to operate it from 240 without consulting the manufacturer, as the heating elements would probably need to be changed.

Sent from my XT1585 using Tapatalk

I understand- however my question is more around how the manufacturer derives that rated current. Maybe I am not phrasing it well.
 
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