Jimmy7
Senior Member
- Location
- Boston, MA
- Occupation
- Electrician
Should all the switches used for say a pool motor be HP rated?
Yes
Disconnects
- Thread starter Jimmy7
- Start date
James L
Senior Member
- Location
- Kansas Cty, Mo, USA
- Occupation
- Electrician
Here's a 40-amp Leviton
120v 2hp
240v 5hp
480v 10hp
600v 15hp
MS402-DS
120v 2hp
240v 5hp
480v 10hp
600v 15hp
MS402-DS
James L
Senior Member
- Location
- Kansas Cty, Mo, USA
- Occupation
- Electrician
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Those come in other configurations, too, like 3ph and DPDT. I used a DPDT-center-off version for a two-speed motor I had refurbished for a delicatessen remodel.
Jimmy7
Senior Member
- Location
- Boston, MA
- Occupation
- Electrician
Looks like a VFD-driven pool pump. The breaker serving the drive will serve as the disconnect. The drive will determine the breaker size.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
The owner want a switch. They are usually 2 speed motors. Check the dp switch 20 amp and see if it has a homeowner rating.
Books will tell you that 745.69 Watts = 1 HP but with losses usually around 1,000 Watts = 1 HP. 230 volts × 5.6 amps = 1,288 Watts that ÷ by 1,000 tells you that is around a 1.288 HP motor at full speed. Like another person posted if that was on a VFD you would have to add the power lost from drive. By the way I do not trust spec sheets or ratings for anything made in cheating china. A U tube video showed where a person tested at least ten made in China LED flashlights & NI Cad batteries. Not one meet what product was labeled for. Some cheated by over 30%.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Remember the HP rating of a device is its ability to Make and Break motor starting currents. This is why General Purpose snap switches need to have an amount of derating when used with motors. Small motors have lower and shorter duration starting currents.
Most local disconnect switches are intended for isolation purposes not starting motors directly. This is partly why pull out style disconnects are often used as HVAC disconnects where the starting function is performed by contactors after power has been applied.
Most local disconnect switches are intended for isolation purposes not starting motors directly. This is partly why pull out style disconnects are often used as HVAC disconnects where the starting function is performed by contactors after power has been applied.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
General purpose AC rated snap switches** can be used for motors, so long as the motor amps is no more than 80% of the switch amp rating.
So the inverse of 80% is 125%, ergo if you use this rule, you automatically exceed the 115% minimum requirement.
The 115% applies to switches that ALREADY have a motor HP rating in their listing, in other words you are not using a general purpose switch, you are using a special purpose MOTOR rated switch. In that case, the 115% over sizing would apply, but is likely already baked into the product listing anyway. So you can double check if you like, but trust me, it will meet or exceed the NEC requirement if it already has a HP rating.
So bottom line: if you use a switch that HAS a HP rating, you know that you are covered. If you want to use a GP snap switch, you have to make sure you are not using it at more than 80% of it's rating. Personally, I just always make sure any switch I use on a motor circuit has a HP rating that meets or exceeds the motor HP I am using. Safest bet.
If you want to see it all, this info is all laid out in 404.14, then basically repeated in 430.83 and 430.109
**Weirdly, if a snap switch is rated for ONLY use with AC, it can be rated for 80% motor amps. But if the switch has an AC/DC rating, you are limited to 50%.