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High current 120v breakers ....

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LAN_403

Vigh holtage

Thu Dec 28 2017, 02:59PM

Registered Member #61739 Joined: Wed Aug 23 2017, 04:43PM
Location:
Posts: 44

Ok i have a 30 amp 120 volt breaker now installed and wired to a steel outlet 3 feet from the breaker box....

The outlet is wired with 10awg thhn wire to the breaker box.

My question is , can i use a 20 amp receptical like this ...

Vigh holtage

Thu Dec 28 2017, 03:05PM

Registered Member #61739 Joined: Wed Aug 23 2017, 04:43PM
Location:
Posts: 44

Will it hold up ?

Or do i need to swap to a nema L5-30 twist lock like generators have ?

My plan is to run 25 feet of 10-3 awg power wire to my 3 kva variac to power transformer banks and sutch ...

I was having srs voltage drop issues and extention cord heating with a standard receptical.

Ohh and when i changed the outlet to the new 20amp one in the pic i saw that the old one had 2 white wires and no ground and bolth white wires were only 14-16 awg , that issue was fixed ... i pulled the wireing and breaker and replaced it with 30a 120 v breaker and 10awg wire, however that receptical is only 20 amp rated.

Will 10-3 power cord for a generator be good for 25 feet @ 120v 30amp without voltage drop ???

Patrick

Thu Dec 28 2017, 05:46PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Generally you'd want 240 vac, that'll cut your drop by half.

klugesmith

Thu Dec 28 2017, 09:25PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

>> Will 10-3 power cord for a generator be good for 25 feet @ 120v 30amp without voltage drop ???

Duh, work it out from scratch. Or use one of many online calculators. At 30 amps your voltage drop would be less than 1.5%.

>>Generally you'd want 240 vac, that'll cut your drop by half.

Yup. If you can change the breakers and load to 240 V, the current can be halved, and the wire can be reduced by 6 AWG steps for the same percent voltage drop and same wire temperature rise. It would be more compelling if you had to run 100 feet.

>> Will it hold up ?
>> Or do i need to swap to a nema L5-30 twist lock like generators have ?

It's against code to use a 20 amp receptacle in a circuit with 30 amp breaker. In case of a fire, your insurance company would tell you to get lost.

Looks like there _is_ a straight blade NEMA option for 30 amps, though I think the twist-and-lock is much more common.

Justin

Fri Dec 29 2017, 08:53AM

Registered Member #46164 Joined: Wed May 07 2014, 08:16AM
Location: California, USA
Posts: 89

I'd get an L5-30 receptacle, or a L6-30 receptacle if you want 240 w/o neutral.

Vigh holtage

Fri Dec 29 2017, 11:55AM

Registered Member #61739 Joined: Wed Aug 23 2017, 04:43PM
Location:
Posts: 44

I can run 240 but i would need to strip down the entire finished product and restart from scratch,

Right now it is a 3kva 30amp continuos dutie variac and then a 3kva 120 to 120/240 isolation transformer tottaly enclosed with switches to select output voltage range

I would have to start over and install 240 30a breakers then still buy new recepticals and plugs then run the isolation transformer in reverse and loose the ability to select taps as it would be a 240/120 to 120 step down , then the variac and then all my meters and a new box and filtering, after i would be useing a 240 outlet but still only getting 120v at 30 amps

A 2 gang 240 or supper beefy 240 variac is tottaly beond my walet ! The big ole 30 a 120 v i got in broken condition , the case and wireing was jacked up but is is in good condition for verry cheap soo ...

This is why i was asking the best way to reduce the drop from a 120 high current breaker.

Seems my best option is to change out to nema L5-30 outlet and twist lock recptical plugs then make a 25 ft 10-3 or better extention cord to the variac

Vigh holtage

Fri Dec 29 2017, 12:05PM

Registered Member #61739 Joined: Wed Aug 23 2017, 04:43PM
Location:
Posts: 44

In the future my ultimate goal here is installing a 30-50 amp 240 volt seperate breaker box that runs to a rotary phase converter for 3 phase power , i have a few of the componants to make it but will take me years to gather the parts ..... but the 240v high current seperate panel for my lab is my next project, then the rotary converter useing a huge 3 phase motor i have 5pluss hp !

I am stopping all projects and focusing on building a decent power system starting from the breaker box and ending at the variac out put in my lab .

For now i want to be able to pull 120v @ 30amps about 25feet without drop under load so i can step it up to 330v 7ish amp or just run it at 120 via swtched output.

klugesmith

Fri Dec 29 2017, 06:26PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

"Without drop under load" is impossible, since you can't afford a superconducting extension cord.
What your solution has is tolerable voltage drop under load. As stated above: 25 feet of 10 AWG, out and back, should lose less than 1.5%.

For cord-and-plug connected appliances, 1.5 percent is usually considered to be fine. Smaller than ordinary fluctuations in the voltage from your electricity provider. At 30 amps, you would have about 3.6 kVA going to the load, and 54 watts heating the cord & its connectors.

How soon can you connect a test load (perhaps some space heaters, toasters, or MWO's), then measure and report the actual voltage drop of your installation? It will creep up slightly as the cord gets warm.

Vigh holtage

Sun Dec 31 2017, 06:17PM

Registered Member #61739 Joined: Wed Aug 23 2017, 04:43PM
Location:
Posts: 44

Ok i will take the advice to swap to a 240v 50a breaker and a 240 twist lock.

This way i can wire my device for 120 v and just leave one termal empty on the devices twist lock male end and still get 120v from the 240 outlet

Pluss i will be ready with 240v for later on with a 2 gang variac

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