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UTS6H - load phases and neutral bond?

APC UPS for Home and Office Forum

Schneider Electric support forum for our APC offers including Home Office UPS, Surge Protectors, UTS, software and services and associated products designed to share knowledge, installation, and configuration.

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MikeyB_apc
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UTS6H - load phases and neutral bond?

This was originally posted on APC forums on 10/10/2015


First, my apologies for asking questions that have probably been asked before.  I tried the search function but it does not appear to be working right now.

I'm about to install a UTS6H to use with either my EU3000is or two paralleled EU2000is's.  I own all three generators.

I was excited to discover this innovative product that will accept a 120V generator input, but I have two questions.

The UTS6H will support six 120V loads.  Can these loads be from both phases of the main panel?  What are the rules, if any, about selecting and balancing the 120V loads?

Second question.  Where is the neutral bond when under generator power?  The neutral bond is in the main panel under utility power and should be (I think) in the UTS6H when under generator power.  I'd appreciate an explanation of the UTS6H design and the neutral bond.

Thank you!!!!

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RussellB_apc
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Re: UTS6H - load phases and neutral bond?

This was originally posted on APC forums on 7/3/2017


According to APC, the various UTS models don't require bonding because of their use of fuses, rather than resetable circuit breakers, like those found in most home panels, as overload protection devices.

See Answer In Context

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MikeyB_apc
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Re: UTS6H - load phases and neutral bond?

This was originally posted on APC forums on 10/11/2015


OK, I've been clicking around here and have answered my second question myself.  Neutral and ground are separated in the UTS6H and the neutral to ground bonding remains in the main panel.  This is a different electrical architecture than with a conventional manual transfer switch and sub-panel where the neutral bond must be made in the sub-panel under generator power and lifted in the sub-panel when under utility power.

It's taken me a while to grasp what the UTS6H actually is.  What it's not is a sub-panel.  It is in effect part of the main panel with (solid state?) relays in series between the load side of the main panel breakers and the load.  These relays can feed the load with either utility power or backup power from a generator or from a UPS.

I assume the designers of the UTS6H selected relays that have no failure mode that would allow backfeeding of generator power to the utility side of the main panel.  I would hope so anyway.  In the case of a power outage I will probably shut off the main panel breaker and the six load breakers anyway though I can see from the documentation none of that should be necessary.

Now I understand this I guess I can also answer my first question.  The six UTS6H circuits can be installed on any 15A or 20A breakers in the main panel regardless of phase as the loads don't care which leg of the main panel the breaker is installed on when they're being fed with generator power via the relays in the UTS6H.

If I have any of this wrong please jump in with a correction.  Thanks!

RussellB_apc
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Re: UTS6H - load phases and neutral bond?

This was originally posted on APC forums on 7/3/2017


"This is a different electrical architecture than with a conventional manual transfer switch and sub-panel where the neutral bond must be made in the sub-panel under generator power and lifted in the sub-panel when under utility power."

Bonding normally doesn't occur in the manual transfer switch as when on utility power, the neutral and ground wires in the manual transfer switch lead back to the main panel where such bonding between the neutral and ground buses occur.

I may be mistaken but under generator power isn't that bonding happening in the generator itself?

"I assume the designers of the UTS6H selected relays that have no failure mode that would allow backfeeding of generator power to the utility side of the main panel.  I would hope so anyway."

The UTS6H's UL-1008 certification mandates that such backfeeding (i.e. why we have a transfer switch, manual or automatic in the first place) cannot occur. Isolation of the generator load from the utility load is mandatory, never shall the two cross paths, at least in not only most transfer switches, but definitely those UL-1008 certified as this one is.

RussellB_apc
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Re: UTS6H - load phases and neutral bond?

This was originally posted on APC forums on 7/3/2017


I'd like to clarrify some things.  First of all the purpose for bonding: it ties back to the circuit breakers in the main panel being able to work propertly, but determine the rapid change in electrical potential in a circuit, that is best detected when neutral and ground are connected in the main panel only.

For [portable] generators like the Honda inverter, the circuit on this device is your main panel, so to speak when you are running off of it in a power outtage.  Sadly, most portable generator manufacturers have what's called a floating neutral, or one where neutral and ground aren't connected, even though they should.

The user can made this happen my making an "Edison" plug,

http://ricksdiy.com/generators/portable-inverter-generator-neutral-ground-bonding-plug-honda-yamaha/

RussellB_apc
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Re: UTS6H - load phases and neutral bond?

This was originally posted on APC forums on 7/3/2017


ok, yet another caveat.  The wiring diagrams for all the APC UTS' suggest not bonding the generator.  Perhaps the UTS does this when working off of generator power only.

RussellB_apc
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246

Re: UTS6H - load phases and neutral bond?

This was originally posted on APC forums on 7/3/2017


According to APC, the various UTS models don't require bonding because of their use of fuses, rather than resetable circuit breakers, like those found in most home panels, as overload protection devices.