Seperately derived power systems?

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VOICECOILS

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Im having trouble understanding this type of powering typiclly found in recording studios and broadcast radio booths known as sperately derived systems. Where 60 volts to ground are measured on each leg, 120 volts is the summed voltage between the two legs. Is this type of power created by a transformer? And if so, are these usally huge transformers? or smaller variables?
 
I agree

I agree

That is what I thought. and it makes sense. My issue now is finding the transformer, my supplier seems to NOT know what Im talking about and tells me no such thing exists. So I suppose I may try another supplier or yell at them for not doing a good job of finding me the right materials.

I have years in the field, but never have I wired up a studio before. Intreresting.
 
With that reading it sounds a bit like one leg was not bonded to ground. and you have an SDS with an unbonded 120v secondary, but I could sure be incorrect.
What do you think, Bob ?
 
augie47 said:
With that reading it sounds a bit like one leg was not bonded to ground. and you have an SDS with an unbonded 120v secondary, but I could sure be incorrect.
What do you think, Bob ?
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OP is talking about a 120 volt transformer with a center tap (60 volt to each other line) being the grounded point.

I have not run into one myself, but this has come up on this forum a few times and appears to be used for controls sometimes also.

I think there is even a code section that mentions such a system somewhere but seem to have difficulty finding it. May have been somewhere in ch 6 or 7 even. If I find something I will post it.
 
augie47 said:
With that reading it sounds a bit like one leg was not bonded to ground. and you have an SDS with an unbonded 120v secondary, but I could sure be incorrect.
What do you think, Bob ?
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Gus, this would be an article 647 system and is simply a center tapped 120 winding. The circuits to the receptacles consist of two 60 volt legs and a grounded conductor.

Roger
 
roger said:
Gus, this would be an article 647 system and is simply a center tapped 120 winding. The circuits to the receptacles consist of two 60 volt legs and a grounded conductor.

Roger
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That is it. I was trying to search both NEC and this site but was either coming up with too many search results or none at all, depending on the search criteria. Thanks.
 
roger said:
Gus, this would be an article 647 system and is simply a center tapped 120 winding. The circuits to the receptacles consist of two 60 volt legs and a grounded conductor.

Roger
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grounding???

A grounded conductor would serve no purpose for 120V loads.
 
Smart $ said:
grounding???

A grounded conductor would serve no purpose for 120V loads.
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Well, actually it would serve the same purpose but in reallity I agree with you, I'm just pointing out what the article is saying in 647.3.

647.3 General.
Use of a separately derived 120-volt single-phase 3-wire system with 60 volts on each of two ungrounded conductors to a grounded neutral conductor shall be permitted for the purpose of reducing objectionable noise in sensitive electronic equipment locations, provided the following conditions apply:
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Roger
 
New area for me, Thanks, guys.
(I originally had a brain-fart and didn't rrealize 60 was 1/2 of 120 and thought it was a floating voltage) DUH !
 
Smart $ said:
grounding???

A grounded conductor would serve no purpose for 120V loads.
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The system still has a "grounded" conductor.

A 120 volt circuit connected to said system does not utilize the "grounded" conductor.

The "equipment grounding" conductor is still connected to the "grounded" conductor typically somewhere at or near the source.
 
kwired said:
The system still has a "grounded" conductor.

A 120 volt circuit connected to said system does not utilize the "grounded" conductor.
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And whether used or not, that grounded conductor is also the neutral conductor in this circuit. Just as the grounded conductor is also the neutral conductor in a 240 volt split phase circuit.
 
kwired said:
The system still has a "grounded" conductor.

A 120 volt circuit connected to said system does not utilize the "grounded" conductor.

The "equipment grounding" conductor is still connected to the "grounded" conductor typically somewhere at or near the source.
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GoldDigger said:
And whether used or not, that grounded conductor is also the neutral conductor in this circuit. Just as the grounded conductor is also the neutral conductor in a 240 volt split phase circuit.
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Uhh... the main reason for pointing it out is that you wouldn't be connecting it to the grounded conductor terminal of a typical 120V receptacle.

...and using isolated ground receptacles and wiring methods may be truly beneficial.
 
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Smart $ said:
Uhh... the main reason for pointing it out is that you wouldn't be connecting it to the grounded conductor terminal of a typical 120V receptacle.

...and using isolated ground receptacles may be truly beneficial.
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Those "bug" receptacle testers will not like what they see if plugged into a system with this kind of supply, and if they have a GFCI tester may not draw enough at 60 volts to trip the GFCI, even though everything is working as intended. I can just see some OSHA or Department of Labor inspector testing one of those and raising a big fuss over the "failed" test.
 
Smart $ said:
Uhh... the main reason for pointing it out is that you wouldn't be connecting it to the grounded conductor terminal of a typical 120V receptacle.
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What type of receptacle would you consider reasonable or standard for this type of system, since one which has a wide slot to distinguish the grounded conductor would be misleading given that the actual grounded conductor does not appear anywhere?
I am not familiar with the application of isolated ground receptacles in a situation where the actual grounding conductor on the receptacle may be just an ordinary EGC connection.
 
GoldDigger said:
What type of receptacle would you consider reasonable or standard for this type of system, since one which has a wide slot to distinguish the grounded conductor would be misleading given that the actual grounded conductor does not appear anywhere?
I am not familiar with the application of isolated ground receptacles in a situation where the actual grounding conductor on the receptacle may be just an ordinary EGC connection.
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I think all he meant was you will not be connecting the neutral of this 60 volt system to the terminal otherwise intended for a conventional neutral. Instead you will have one ungrounded conductor on that terminal and the other ungrounded conductor on the traditional "hot" terminal. Both will operate at 60 volts to the EGC, both will have overcurrent protection somewhere ahead of the device. The load still sees 120 volts and don't care that it is only 60 volts to ground.
 
kwired said:
I think all he meant was you will not be connecting the neutral of this 60 volt system to the terminal otherwise intended for a conventional neutral. Instead you will have one ungrounded conductor on that terminal and the other ungrounded conductor on the traditional "hot" terminal. Both will operate at 60 volts to the EGC, both will have overcurrent protection somewhere ahead of the device. The load still sees 120 volts and don't care that it is only 60 volts to ground.
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One reason for the wide prong plugs on equipment is to insure that a particular part of the wiring/controls/etc. is operating not far from ground. Is the reduction from 120 volts to 60 volts good enough to maintain the UL listing of equipment that is required to have a polarized plug and cord set? (Think of Edison base light bulb sockets.) Or should you just be careful not plug such equipment into a balanced receptacle?
My impression is that a balanced distribution system is used for specific types of loads or environments, and just plugging random conventional loads into that system would not be a good idea anyway?

And then, just to muddy the waters further, there is the separate topic of older RV inverters and some current MSW inverters which produce "balanced" power just to reduce the cost of the electronics. :) Attach them to a wiring system with a ground-to-"neutral" bond, and the magic smoke comes pouring out.
 
exactly

exactly

don_resqcapt19 said:
This is often called a "balanced power" system.
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This is true as all the audio line signals consist of balanced circuits. so to have balanced power would have the most rejection to hums and noises that the audio equipment will emit if the service is un-balanced. Professional studios require this as the equipment itself cannot be noisy or have 60hz hum by all means. Typiclly caused by ground loops and or induction to the audio circuits.

I need help finding a good transformer for this application.

Thanks for your help dudes
 
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