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240 V Circuit- What Size?




 
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Author Topic: 240 V Circuit- What Size?  (Read 1715 times)
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Carl WA1KPD
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« on: March 03, 2018, 02:14:40 PM »

Hi,
Setting up the new QTH in an old farmhouse in Maine. Im going to have an electrician run a 240V line to the ham shack to run
a linear rather then straining the old wiring.
Right now I am using a AL-80B and the manual says "This amplifier uses two 10A fuses for 240 Vac operation." That would seem to me to indicate that a 15 amp circuit should be sufficient? I don't plan on running higher power.
In addition, can the electrician split off of the 240 line in the shack and also provide 120V for the exciter and misc accessories?
Your input is appreciated
Carl
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« Reply #1 on: March 03, 2018, 02:51:51 PM »

You can run a 10ga 4 conductor cable to a small sub-panel.  From the sub-panel you can get 240v through a twin 15amp breaker. 120v can be through a single 15amp breaker and the neutral.  The 4th wire is the ground conductor.  You would have to run the 10ga cable from your main-bldg AC panel.

If you don't want to spend that much on 10ga cable you could use 12ga, but I wouldn't use anything smaller than 12ga.  You could also just run the cable into an oversize electrical box and have the 240v outlet and the 120v outlet in the one box.  This eliminates the sub-panel and breakers.  You would still need the 4 conductor cable (3 wires plus the ground).

Fred
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WD4DMZ
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« Reply #2 on: March 03, 2018, 04:51:35 PM »

Years ago I built a hobby room in my attic that required a 35 foot run from the main panel to the center of my attic. For the 35 foot run I used 3 conductor plus ground 8 gauge into a small sub panel. From there I fanned out with three 12 gauge 20 amp 120VAC circuits to run my shack, a window AC unit and then four separate 120 VAC outlets.

The AL80 family is advertised to work on a standard 14 gauge 15A 120VAC circuit. When I first used my AL80 on an existing 15A 120VAC the voltage drop was very noticeable and everything on that circuit was affected. Because of that I used only 12 gauge for the new shack.

On the 20 amp 12 gauge 120VAC circuit the voltage drop when using the AL80 is very small. Nothing else is connected to my sub panel other than my hobby room stuff. Since everything worked fine with that arrangement I never put the 2 pole 240VAC circuit in for the AL80 and all has been fine.

The 8 gauge may be overkill as it is protected by a 30A two pole breaker. But, there is little voltage drop so is worth the extra $$.

Consider running the AL80B on 120VAC.

If you ever decide you need more power, such as an AL with max legal power, run the 3 wire 240VAC circuit now and do as I did from the sub panel. Also, use 12 gauge wire even if you choose to protect it with a 15 amp breaker. The cost difference between 14 gauge and 12 gauge wire is not that much.

Rich
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« Reply #3 on: March 03, 2018, 08:17:29 PM »

  When my CA tract home was built in 1945 it had a 30 amp 120 volt service which served me well, drier, stove, water heater and floor furnace were all gas, about 10 years ago I had a 150 amp service installed. The shack is in the garage and service  panel on the other side of the house. The electrician suggested a 50 amp sub panel in the garage which I went with.

   I wired out of there for the garage and shack. I have a dedicated 15 amp 220 volt circuit for my Heath kit HL-2200 amp which works fine. I have a dedicated 20 amp 120 volt circuit for the T-368 and then other 120 circuits for the rest of the garage and shack.

   Looking back now I should have put in a dedicated 120 volt circuit with a variac on it for the old boat anchor equipment. I was also given a number of 30 amp 120 volt relays, it would be nice to have ALL the shack loads to one switch that will kill all the shack outlets.
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« Reply #4 on: March 03, 2018, 08:24:22 PM »


Your biggest cost is to have the 'lectrician show up to work.  You also mention that the wiring is in an "old farmhouse". So it seems that you don't trust the wiring 'as is'. I wouldn't trust it, unless you rip the walls apart to inspect it..... but anyways, get your shack rewired up to code.

 If it was me specking the job, The Minimum would be a 20A, 240V ckt for your amp, a separate ckt for your lights, and (2) 20A 120V ckts for the rest. (its kinda nice to have lights after you trip the breaker in your shack). And I'm not going to guess if you have heat in the shack...

You could do a real nice job with the subpanel and 12 AWG ckts.

klc
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wa1knx
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« Reply #5 on: March 03, 2018, 11:58:36 PM »

Carl
      I grew up in Me,, I have a 40' run of #10 and 15A breakers. Larger wire = less dimming. but cha might wanna also
run a 10a circuit for the big bug zapper you'll need up theya in maine deaya!!
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Carl WA1KPD
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« Reply #6 on: March 04, 2018, 04:50:47 AM »

Thanks,  lots of good info.
The total run is about 25 ft from basement panel to 2nd floor room. Ceiling light is independent run off BX, appears to be part of first wiring .ca 1930. Wall outlets are romex about 1970.
Carl

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« Reply #7 on: March 04, 2018, 11:31:48 AM »

Where it me (I'm the electrician here), I'd do a minimum of 10 gauge.  Into a panel, then you can have a couple branch circuits.

Even if you just make a single run of ten gauge today, you can add a sub panel down the road for a legal limit amp, plus a power supply and rig.

I recommend ten gauge because of the difference when one is hit by electricity.  There is a YUUUUGE difference between getting shocked by a 14, 12 and 10 GA circuit.  Because of resistance in the wire.

Dynamic regulation of that amplifier on peaks is partially determined by the round resistance value to the pole pig.  Don't cheap out and lose a hundred watts and increase imd because you 'only' ran a 15A circuit.

My radio shop is a 100A feed, but I also run more :-)


Voltage drop figured, to your panel on the 25 foot run 14 vs 10 posted.  Both would be within spec.  14 gauge you couldn't add very much at all before it was overloaded.  10, you could add another couple amps!  Cost, probably another 10 pct overall.



--Shane
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Carl WA1KPD
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« Reply #8 on: March 04, 2018, 12:08:45 PM »

Shane,
I don't plan on a panel in the shack, so assuming I go with #10, what size breaker would you put in?
 
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« Reply #9 on: March 04, 2018, 01:20:19 PM »

Shane,
I don't plan on a panel in the shack, so assuming I go with #10, what size breaker would you put in?
 

30amp two pole breaker in your main panel in the basement.  3 conductors plus the ground to get 240v in the shack.  120v outlets can be added off the 4 conductor cable
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« Reply #10 on: March 04, 2018, 02:49:05 PM »

#10 can be fused up to 30 amps.

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w4bfs
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« Reply #11 on: March 05, 2018, 03:26:08 AM »

Shane,
I don't plan on a panel in the shack, so assuming I go with #10, what size breaker would you put in?
 

according to my understanding of the NEC a branch circuit ampacity is limited by the lowest ampacity in the branch  ie  you can run 10 ga wiring but if you tie a 15 Amp receptacle on it the maxmum branch current is 15 Amps with a few exceptions such as some inspectors will allow 20 Amp branch circuits with 15 Amp 120V duplex receptacles.  This is why if you want 30 Amps and 120 V branches you will need a subpanel   
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« Reply #12 on: March 05, 2018, 09:58:23 AM »

BFS is correct. If you run a #10 you will need a sub panel. Terminating a #10 on an outlet will not work.

One choice is to use a really inexpensive two fuse box. You could run two #12 or #14 lines out of it to outlets.

However, if you have space in your main panel for a two pole breaker, you also have space for two one pole breakers. A really easy option is to run two #12 120VAC lines off of 20A breakers. The AL80B will run fine on 120VAC. Use one line for the AL80B and the other for all of your other loads. You will not see any flickering in the other line that way and the voltage drop to the AL80B will be very small.

I ran out of space in my panel so used the slim 1/2 width breakers for lighting circuits to create space for the two pole breaker that feeds my shack. Older panels may not accommate 1/2 size breakers so check that out.

Rich
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« Reply #13 on: March 05, 2018, 10:25:25 AM »

You will NOT need a subpanel for #10. You will need to put a 30 amp receptacle at the end, or a 15 or 20 A breaker in the main panel if using a 15 or 20A rated plug.

It's the terminated plug size, not wire size, that determines fusing (circuit breaker).  Of course, you can always terminate it with a 30 amp rated dryer type receptacle, but use a 15 amp breaker.  

A subpanel will be needed if you want to legally split that into branch circuits in the shop.

The idea of a pair of 20 amp circuits is appealing.  However, you must have them run with a handle tied breaker (240 volt style) if they will be in the same sheath or be run as a branch together. 

--Shane
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KE7NL - Jack
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« Reply #14 on: March 05, 2018, 02:23:10 PM »

Whatever the "CODE" dictates for wire size, I would use a size larger.
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« Reply #15 on: March 07, 2018, 01:17:35 PM »

I considered how much power was needed then doubled it when installing the capacity. Almost no voltage drop, maybe 2 volts.
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