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[Jeremy Young]

Hello folks.  I have some electrical questions below.  I want to preface by saying that I live in Canada, I am not an electrician, and i won't hold anyone liable for any guidance they give me.  i will consult an electrician for the execution of my plans, but i'm at the brainstorming stage and i trust everyone's experience on here for the context of my needs.


I just bought some new power amps (yay).  one of them came with a 20a power cord, which won't plug into anything i have (boo).  The amp is a Crest Prolite 7.5 and i'm currently only using one channel of it on a 4-ohm load for the subwoofer i own (EAW FR250z).  my plan was to use this for my sub for now, until my next buying spree (new subs) where i can use it in stereo with 4-ohm loads per channel.  i understand that although the fancy silkscreening on the amp says it's a "professional 7500w power amplifier" that it's not actually drawing 7,500 watts all the time, or hardly ever (signal level and dynamic range affecting this of course). 


many of the venues i frequent only have 15a type receptacles (nema 5-15), and i'm starting to get concerned about being able to plug this thing in anywhere i go.  i've built a temporary adapter just so i can test the amp at low volumes, using a 14ga wire into a nema 5-20 receptacle. at first i thought 12a would be a  better choice for the 20a load, but realizing that the upstream cable is likely 14a since it's a 15a breaker, this didn't seem pressing for my needs at the time.  however, i want to make a more permanent solution to my problem before gigging with the new amp.


i already own a power distro (sub panel screwed to some ¾" plywood with a handle and a nema 14-50 "stove plug" on a short lead).  the subpanel has two 4x4 boxes off it connected with bx cable, each with a pair of nema 5-15 duplex receptacles, going back to four 15a breakers.  i didn't build this distro, but since doing some research i'm starting to get more and more confused about how it was built.  it used to live in a venue i worked at, but it was replaced by something with more power when we upgraded the system and i inherited it.  first off, i would consider this a 4-channel 60a panel (simply 4 x 15a), however, after closer inspection it seems that the electrician who built this used a plug (the 14-50) with a wire rated for 40a.  the silkscreening is almost all worn off, but what i could make out definitely says 40a (but does not say the gauge anywhere legibly).  my initial idea was to simply replace one of the 15a breakers with a 20a breaker, toss in a new receptacle and i'm set for anywhere i can find a 14-50 to plug into.   after some reading, i'm seeing that those plugs are typically 50a.  so.....i have four 15a breakers totalling 60a, on a wire rated for 40a with a connection rated for 50a...confused yet?  to top it all off, the four breakers are attached to each other (siemens brand) and the middle two are connected at the "switch" (for lack of the correct terminology) which i believe makes it a common trip type...but i don't see where the hot leads enter the middle two breakers (the two hot leads only seem to connect to the outside two breakers, which are definitely connected to separate duplex receptacles which seem to get power through some type of internal wire or black magic).  so now i'm thinking maybe i should replace the plug end to something rated for the full 60a, replace all four 15a breakers with three 20a, upgrade the wire to 12a  and receptacles to 5-20, and then each of my power amps would have their own 20a supply (i have three stereo amps total, the other two being the Crest Prolite 3.0's with 15a cords). 


i guess my question is, does what i'm seeing in this panel make sense?  can i replace that block of four breakers with three?  what's the purpose of having a common trip on separate circuits?  is there a more common plug i should use to supply the subpanel other than the stove plug? (sorry this might be more of a regional specific question that no one can answer for me).  if i run my amp off a 15a circuit with an upgraded version of my adapter (using 12ga or better this time) am i risking damage to the amp (i presume it would clip earlier) or does that become a fire hazard since the 15a breaker and wire would not be rated for those kind of currents?  is there a better approach i should be taking for a portable setup like mine? 


thanks in advance!  If people need pictures, i'm sure i can figure out how to post some.

[Mark Cadwallader]

I am not a licensed electrician either, but a NEMA 14-50 plug has two 50a legs, nominally supplying 100a at 120 volts. I would hope and expect that the load is split so there are two 15a breakers per leg, for a maximum of 30a per leg.

That said, my layman's understanding is that you distro (as described) does not conform to the (USA's) National Electrical Code. (The NEC is somewhat mis-named; it is a model code that states and local governments may adopt and enforce, but it does not carry the force of law unless and until it is adopted.). There are others here who can provide a better, more detailed explanation of why your distro doesn't meet the NEC, but the use of wire not rated for 50a is a problem. Mark C.

[Ray Aberle]

Hi Jeremy,

Great set of questions! To start with, a range plug (NEMA 14-50) is a great option for small distros- lots of venues have them, and the ones that don't probably could add one easily.

What Mark said about 100A actually there. You're using a 50A/220V input, so you have 50A per leg. Now you mentioned some "common trip" breakers-- if these are indeed 15A/220V breakers, seems silly that they would be running to multiple outlets with that-- it would be better to have separate single pole breakers for each outlet you want to use. If you have different things on the two sides of the "common trip" breaker, it would suck to have one get overloaded and trip, and kill the other circuit at the same time!

The quick and easy adapter to make is a 5266C male (15A/125V) connector over a length of 12/3 SOOW to a 5-20R 20A/125V female connector. Your amp then plugs into that. Even though the receptacles are 15A, you're probably still on a 20A breaker, although you never know the gauge of wiring between the panel and the outlet, or the distances involved. However, when using your distro, you will definitely want to install 20A breakers and 20A receptacles. Since you've fussed at a venue to get the 50A circuit anyways, best to make sure you can use it to its full potential!

Load Balancing: Make sure you balance the load as best as you can between the 50A legs. You don't necessarily have to limit your breaker options to something that adds up to 100A -- you're most likely not going to be maxing them out ever. (It's like your house: Your 200A/220V panel has breakers that add up to more then 200A -- but your main never trips. Because you are not maxing out all of those circuits!) Having specific breakers and outlets for certain things is a wise precaution. That way, you label the outlets with what gets plugged in there, and you have the comfort of knowing things are balanced and consistent from show to show.

That Input Lead: I'd want to check it out and see if it's 6/4 or 4/4 (or *gasp* even 8/4) wire-- it should be a rubber jacketed SOOW cable again. If it's a household install wire (thin black coating, you can see the internal conductors twisting around) that is NOT what you want to be using.

If you ever make it down to the Seattle area, hit me up and we can look at what you got closer.

-Ray

[Jonathan Johnson]

In many cases, the ONLY difference between a NEMA 5-15 (15A) receptacle and a NEMA 5-20 (20A) receptacle is the design of the face. The internal terminals and wiring interface is the same. It is common to install NEMA 5-15 receptacles on a 20A circuit, and it is allowed by the National Electrical Code in the United States (don't know about Canada). So in many cases, you should be safe to use a 5-15P to 5-20R adapter that's wired with 12AWG wire. The presence of 5-15 receptacles does not necessarily mean that the circuit is rated for 20A. (To be clear, NEMA 5-15 duplex receptacles are typically rated for 20A feed-thru service on the terminal screws.)

However, in residential construction, super-cheap 5-15 duplex receptacles (about $1/ea or less) are available, and these most likely do NOT have internal contacts that are rated for 20A.

If you do use a 5-15P to 5-20R adapter, it would be best to have some kind of current limiting device (breaker or fuse) that protects to 15A. That way you can be assured that you are not overloading a receptacle that's not designed for 20A loads but has been installed on a 20A circuit.

(P.S. -- the "P" suffix in 5-15P refers to "Plug" or male component; the "R" suffix in 5-20R refers to "Receptacle" or female component.)

[TJ (Tom) Cornish]

Hello folks.  I have some electrical questions below.  I want to preface by saying that I live in Canada, I am not an electrician, and i won't hold anyone liable for any guidance they give me.  i will consult an electrician for the execution of my plans, but i'm at the brainstorming stage and i trust everyone's experience on here for the context of my needs.


I just bought some new power amps (yay).  one of them came with a 20a power cord, which won't plug into anything i have (boo).  The amp is a Crest Prolite 7.5 and i'm currently only using one channel of it on a 4-ohm load for the subwoofer i own (EAW FR250z).  my plan was to use this for my sub for now, until my next buying spree (new subs) where i can use it in stereo with 4-ohm loads per channel.  i understand that although the fancy silkscreening on the amp says it's a "professional 7500w power amplifier" that it's not actually drawing 7,500 watts all the time, or hardly ever (signal level and dynamic range affecting this of course). 


many of the venues i frequent only have 15a type receptacles (nema 5-15), and i'm starting to get concerned about being able to plug this thing in anywhere i go.  i've built a temporary adapter just so i can test the amp at low volumes, using a 14ga wire into a nema 5-20 receptacle. at first i thought 12a would be a  better choice for the 20a load, but realizing that the upstream cable is likely 14a since it's a 15a breaker, this didn't seem pressing for my needs at the time.  however, i want to make a more permanent solution to my problem before gigging with the new amp.


i already own a power distro (sub panel screwed to some ¾" plywood with a handle and a nema 14-50 "stove plug" on a short lead).  the subpanel has two 4x4 boxes off it connected with bx cable, each with a pair of nema 5-15 duplex receptacles, going back to four 15a breakers.  i didn't build this distro, but since doing some research i'm starting to get more and more confused about how it was built.  it used to live in a venue i worked at, but it was replaced by something with more power when we upgraded the system and i inherited it.  first off, i would consider this a 4-channel 60a panel (simply 4 x 15a), however, after closer inspection it seems that the electrician who built this used a plug (the 14-50) with a wire rated for 40a.  the silkscreening is almost all worn off, but what i could make out definitely says 40a (but does not say the gauge anywhere legibly).  my initial idea was to simply replace one of the 15a breakers with a 20a breaker, toss in a new receptacle and i'm set for anywhere i can find a 14-50 to plug into.   after some reading, i'm seeing that those plugs are typically 50a.  so.....i have four 15a breakers totalling 60a, on a wire rated for 40a with a connection rated for 50a...confused yet?  to top it all off, the four breakers are attached to each other (siemens brand) and the middle two are connected at the "switch" (for lack of the correct terminology) which i believe makes it a common trip type...but i don't see where the hot leads enter the middle two breakers (the two hot leads only seem to connect to the outside two breakers, which are definitely connected to separate duplex receptacles which seem to get power through some type of internal wire or black magic).  so now i'm thinking maybe i should replace the plug end to something rated for the full 60a, replace all four 15a breakers with three 20a, upgrade the wire to 12a  and receptacles to 5-20, and then each of my power amps would have their own 20a supply (i have three stereo amps total, the other two being the Crest Prolite 3.0's with 15a cords). 


i guess my question is, does what i'm seeing in this panel make sense?  can i replace that block of four breakers with three?  what's the purpose of having a common trip on separate circuits?  is there a more common plug i should use to supply the subpanel other than the stove plug? (sorry this might be more of a regional specific question that no one can answer for me).  if i run my amp off a 15a circuit with an upgraded version of my adapter (using 12ga or better this time) am i risking damage to the amp (i presume it would clip earlier) or does that become a fire hazard since the 15a breaker and wire would not be rated for those kind of currents?  is there a better approach i should be taking for a portable setup like mine? 


thanks in advance!  If people need pictures, i'm sure i can figure out how to post some.

Jeremy, I wrote an article on how branch circuit distros work.  It may help you visualize some things: http://tjcornish.com/articles/power-distribution-part-3--.html

[Jeremy Young]

Wow, amazing responses from everyone.  Mark you were the first to point out the oversight in my findings...50A 240v is indeed two 50A legs @ 120v.  thank you for clarifying that for me (rookie mistake).  Ray and Jonathan thank you for your suggestions on adapters and adapter choice (further reinforced by Tom's great article linked above).  Tom I just finished reading all of your articles, great stuff there, wish I'd stumbled on them weeks ago before polluting my mind with awful youtube DIY videos and unhelpful google results.  So much knowledge in these forums...fantastic stuff.  Those R's, P's and L's are making more sense now in the naming schemes.

OK so to summarize, I'm going to upgrade my little adapter with a 12a supply cable and possibly a local current limiting device if I can find something compact enough.  Seems logical and then I'm set for simply plugging my amp into standard 120v sockets. 

As for my distro (or BCD as Tom has put me onto calling it); I think there are a few issues at hand here.  Firstly for my needs, the lack of a 20A circuit.  Secondly the lack of a properly sized supply wire (it's definitely black rubber coated and I can see the internal conductors twisting around inside, time to retire that thing!).  Lastly, that common-trip business (although Tom has some differing thoughts on that in his article).  At the very least, I need some #4 wire and some 20A single pole breakers, and possibly a 50A 240v breaker for some localized protection, I'm practically starting from scratch I guess.  Definitely sold on keeping with the 14-50P though; I have seen them in venues I've frequented, and most houses have at least one so it feels like a safe bet.

I'll do my best to balance the loads on the phases, all good advice here.  I ran some calculations based on my amplifier load impedances and the corresponding ⅓ power consumption ratings; seems like there could be some light load gigs where I can run all three amps on a single 20A circuit without much of an issue, still allowing an additional 20% margin over the rated current draw.  Seems like that adapter will get some good use.

Ray if I find myself crossing the water to your neighbourhood anytime soon I'll definitely hit you up!  Tom I checked out the various websites you linked to for pre-built BCD's, and I can respect the sentiment that a listing could keep me out of trouble; however I didn't find anything that suited what I was looking for (14-50P to multiple 5-20R's, rackmount would be nice).  If anyone has any links they can share I'm interested in exploring some options.

All the best!

[Jeremy Young]

scratch the request for help finding prebuilt options, i did a forum search and found everything i needed.  thanks again everyone!

[Stephen Swaffer]

What Mark said about 100A actually there. You're using a 50A/220V input, so you have 50A per leg. Now you mentioned some "common trip" breakers-- if these are indeed 15A/220V breakers, seems silly that they would be running to multiple outlets with that-- it would be better to have separate single pole breakers for each outlet you want to use. If you have different things on the two sides of the "common trip" breaker, it would suck to have one get overloaded and trip, and kill the other circuit at the same time!

"Code" requires common trip breakers anytime you use a shared neutral.  Shared neutrals have their place-but their use is becoming less and less common because of various issues involved.  In a distro, I see no reason to share a neutral-just run an extra wire for a few inches and eliminate the need for a common trip.

[ProSoundWeb Community]