ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Recent Posts
Run Cap subsitution question. Two vs. one
by LarryC - 05/13/22 08:43 PM
Material shortages???
by NORCAL - 05/02/22 04:12 PM
New in the Gallery:
240/208 to a house
240/208 to a house
by wa2ise, October 9
Now you know.
Now you know.
by Tom_Horne, September 7
Who's Online Now
0 members (), 36 guests, and 11 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Joined: Jul 2004
Posts: 785
LarryC Offline OP
Greetings all.

Had a factory smoke leak at the motor for my air compressor. 7.5 HP WEG single phase motor 240 volt. A start cap decided to leave home and splattered itself all over the inside of the motor junction box. After cleaning out the mess, I checked the bearings and centrifugal switch. All good. I had a local motor shop megger the windings. All good. So I assume the cap failed with age and heat. No significant change with the mechanical load as far as I can tell. Motor is 14 years old.

I decided to replace the start and run caps. Line voltage is usually around 240 when I check it and the caps were rated for 250. I decided to be a bit more cautious and I ordered 330 V caps to replace the existing ones. Of course, no good deed goes unpunished and now I am cramped for space in the box.

The existing run caps are two 30 u in parallel and I was wondering if there was any reason not to replace them with a single 60 u cap.


Joined: Jul 2004
Posts: 9,687
Likes: 10
Electrically it should work fine. I have played some strange capacitor tricks to get the AC going until I could get a new one. I have rooted around in my junk box looking for a bigger capacitor cover.

Greg Fretwell
Joined: Jul 2004
Posts: 785
LarryC Offline OP
My concern is whether the single cap will develop problems because of heat dissipation issues. Two caps, half the current, a quarter of the heat generated, assuming same internal resistance. I am now thinking of staying with dual run caps and just up the sizes of the start caps since they are in the circuit for a much shorter time.

Am I overthinking this?

Link Copied to Clipboard

Tools for Electricians
Tools for Electricians

* * * * * * *

2020 Master Electrician Exam Preparation Combos
2020 NEC Electrician
Exam Prep Combos:
Master / Journeyman


Member Spotlight
Bakersfield, CA (Originally Orange Co.)
Posts: 1,438
Joined: February 2004
Top Posters(30 Days)
LarryC 2
Popular Topics(Views)
291,215 Are you busy
223,716 Re: Forum
209,150 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.5