Should UPS output be treated as SDS?

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sparkyguy545

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Installing a 15 kVA UPS, 208 V, 3-phase input; 208Y/120, 3-phase, 4-wire wye out. The manufacturer's manual does not specifically state, but wouldn't the output be considered a SDS and be treated much like the secondary of a 15 kVA xfmr? By this I mean, shouldn't it require a new GEC? I don't think I've ever seen one installed.
 
To simplify, if you run a neutral to the UPS and this neutral is a solid connection to the output than it is not an SDS.

Some UPS?s will have a transformer on the out put so the bypass and UPS input are 3-wire and is a SDS.
 
brian john said:
To simplify, if you run a neutral to the UPS and this neutral is a solid connection to the output than it is not an SDS.

Some UPS?s will have a transformer on the out put so the bypass and UPS input are 3-wire and is a SDS.
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Same applies to the latter... if a feeder neutral is run and solidly connected to the output, it is not an SDS. It does not matter whether the neutral is connected to the input. The underlying issue is the output must be grounded in a compliant manner.
 
After I re-checked, I must slightly modify my original post. The unit in question is not 3-phase input or output. It is actually a single-phase 208V input and 208/120 single-phase 3-wire output. However, this doesn't change my original question at all.
If anyone cares to investigate, the model is APC SURT15KRMXLT-1TF10K
Input: 208V single-phase with NO neutral connection (2 x Hots, 1 x Gnd)
Output: 208/120 single-phase (2 x Hots, 1 x Neutral, 1 x Gnd)
Literature notes the unit is a "transformer-type", but does NOT say whether the internal transformer is on Input or Output. The O&M manual does not provide any further information either. Where the heck does the Output Neutral come from with no incoming Neutral? How can it not be an SDS if it is a "transformer-type".

When I contacted their customer support by email, I was told in no-uncertain-terms that NO Grounding Electrode Conductor was necessry because that was obtained "from the upstream supply source". Mechanically, there isn't anyplace to connect a GEC anyhow. It obviously isn't designed for it.

If it had an incoming Neutral, I understand it could be a NON-SDS unit. But it doesn't have a Neutral.

Since it has a transformer, it would appear to be a SDS. If it is, the Output "could" have an Equipment Bonding Jumper inside the unit . . . . . but what about the lack of a GEC? The thought occurred to me that they "might" simply bond the Neutral it to the Incoming Source Ground conductor. But that certainly doesn't meet NEC and I wouldn't think it could get a 3rd party listing if that was done.

My IEEE Green Book (Std 142) has an entire Section devoted to the subject of UPS System Grounding (Section 1.9 in my book). It shows (and explains very well) eight different arrangements of UPS grounding & bonding. All of the eight IEEE examples make sense to me as far as NEC is concerned. None of the eight examples seem to fit this unit. It's listed by numerous international third-party agencies.

To me, it doesn't seem to be either Non-SDS, or SDS.
 
Unless I misunderstood your question, looking at the drawing you provided there is a connection for the GEC up at the top terminal strip. It also references Delta 6 - GEC provided by others. Again maybe I misunderstood your question.
 
Fast__Eddie said:
Unless I misunderstood your question, looking at the drawing you provided there is a connection for the GEC up at the top terminal strip. It also references Delta 6 - GEC provided by others. Again maybe I misunderstood your question.
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Which leads me to not understanding. I posted the link to the system wiring diagram to resolve the OP question (...and perhaps to stimulate other questions as well). However, your post is in reply to my post and I did not pose any question :huh:
 
Smart $, I appreciate the link to the manufacturers xfmr schematic.
I downloaded the O&M manual but it did not contain a schematic. Upon review, it now appears clear to me that the xfmr must be on the output of the UPS. The actual UPS is not shown but would be upstream of the transformer. The UPS Inverter/Batteries must consist of a unit with 208 single-phase input and a 208 single-phase output. The UPS output must feed the primary of this xfmr. The xfmr secondary is 208/120 single-phase with a grounded center-tap. IMHO, this transformer is clearly an SDS. I see that the mfr's schematic does show a N-G bond between Terminal #8 and GND. However, for a complete and proper installation, it also requires a GEC to be installed between Neutral and a suitable Grounding Electrode per NEC A250.30(A)(4). This is totally contrary to what I was told by two different people at the mfr's tech support.

I'm going to ignore the email response I got from the mfr and install a suitable GEC plus verify the N-G bond is properly installed.
 
Had that happen to me same with APC. I called and emailed, to get them to show clearly on the documents the GEC, quoting Per 250-30(A)3, on their MGE 250 kVA pdu. The drawing, by omission, and the manual, "change or to and", were both wrong. The unit comissioning document was correct, full one page notice with electrician's signature indicating the GEC is installed per 250-30(A).

The first call, a good guy sent out some older documents that were correct, not unit specific. The calls after that, contract and manufacturer's documents were not correct, and I was told an engineering change could be years.
 
Looked it up again, an MGE PMN084 42 225. Here's the installation manual pdf:

http://www.apcmedia.com/salestools/MBPN-7SPHE4_R0_EN.pdf

and look at page 39 of 58, 3.4.3.1 grounding. It's really worded badly where it calls for the safety ground to originate at the utility service equipment and says "OR" other acceptable building ground, such as the building frame ...

Drawing is on the same page with the same omission, showing the EGC coming in with the feeder with an earth ground symbol. The unit obviously needs both an EGC and a GEC. The drawing needs a GEC on it.

This unit is mated to an adjacent cabinet that is a dual source static switch and the feeders are not sourced at the "service", they originate at DP switchboards, which have an EGC but no GEC available. The "service" point is ~ 80 ft away in a much larger 2N switchboard. There are two redundant 2(N+1) UPS rooms that source the feeders. This is the typical installation.

Interesting artifact. In my mail way prior, I stated that connecting the two different EGC busbars, from two different UPS rooms, together at the static switch would cause a small equalizing current to flow over the EGCs as they came together at the static switch, however connecting an Ibeam to any other I beam in the building with wire similar would cause no current to flow. The EGCs would be noisy and the Ibeams would be quiet. The GEC was necessary because 250-30(A)3 required it and because it serves a different purpose, a clean quiet reference point (low impedance path) to the equipotential earth ground.

The EGCs in place have 4 amps of noise on them in service.

Have at this, does this drawing and paragraph 3.4.3.1 meet code or not.
 
__dan said:
...

Have at this, does this drawing and paragraph 3.4.3.1 meet code or not.
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Drawings and documentation do not have to meet code. The installation and use does.

That said, I think anyone knowledgeable of Code also recognizes that manufacturer's documentation and drawings are created by people not always, and often not totally familiar with Code requirements. Thus, I believe Code requirements take precedence over 110.3(B) issues in conflict.
 
Smart $ said:
Drawings and documentation do not have to meet code. The installation and use does.

That said, I think anyone knowledgeable of Code also recognizes that manufacturer's documentation and drawings are created by people not always, and often not totally familiar with Code requirements. Thus, I believe Code requirements take precedence over 110.3(B) issues in conflict.
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I do not disagree, however the customer's permission is required to go forward with any work. All parties were informed in writing, the customer, the local building official (former carpenters), the engineer. The engineer refused the change and justified it on the manufacturer's drawing. Engineer's drawing had no GEC earth ground symbol on it at the transformer secondary. The other parties went that way. As instructed, the GEC was omitted, despite my hitting them early and pretty hard on it.
 
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Fast__Eddie said:
looking at the drawing you provided there is a connection for the GEC up at the top terminal strip. It also references Delta 6 - GEC provided by others.
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there is no doubt in my mind that this is an SDS. In looking at the schematic though, i'm wondering howcome it doesn't show the output neutral bonded to the GEC, unless i'm reading it wrong.
 
__dan said:
I do not disagree, however the customer's permission is required to go forward with any work. All parties were informed in writing, the customer, the local building official (former carpenters), the engineer. The engineer refused the change and justified it on the manufacturer's drawing. Engineer's drawing had no GEC earth ground symbol on it at the transformer secondary. The other parties went that way. As instructed, the GEC was omitted, despite my hitting them early and pretty hard on it.
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Neither the documentation wording nor the drawing exclude the use of a GEC. The wording is in error in that it says the grounding conductor must be insulated. Under the NEC, a grounding conductor is not required to be insulated. Quite trivial though.

More to the point, nothing indicates the specified grounding conductor is to be an EGC. The grounding conductor can just as easily be a GEC and meet all the requirements of the manufacturer's documentation and the NEC.

Also, there is no industry standard GEC earth ground symbol. The ground symbol on the drawing can just as easily reqpresent a GEC as an EGC.

The only place I can see a problem is if the grounding conductor in the optional j-box and 10' cable is undersized for a GEC.
 
djd

djd

Smart $ said:
Neither the documentation wording nor the drawing exclude the use of a GEC. The wording is in error in that it says the grounding conductor must be insulated. Under the NEC, a grounding conductor is not required to be insulated. Quite trivial though.

More to the point, nothing indicates the specified grounding conductor is to be an EGC. The grounding conductor can just as easily be a GEC and meet all the requirements of the manufacturer's documentation and the NEC.

Also, there is no industry standard GEC earth ground symbol. The ground symbol on the drawing can just as easily reqpresent a GEC as an EGC.

The only place I can see a problem is if the grounding conductor in the optional j-box and 10' cable is undersized for a GEC.
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I am thinking this as as I read these responses; could we have both a separtatly derived system and the ups. I always thuoght that was the purpose of an Isolating transformer for an IT room , here we have the ups coupled?
going back to school
 
djd said:
I am thinking this as as I read these responses; could we have both a separtatly derived system and the ups. I always thuoght that was the purpose of an Isolating transformer for an IT room , here we have the ups coupled?
going back to school
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There is nothing in the NEC, at least that I'm aware of, that precludes a power (<1000W) isolation transformer, integral with a piece of equipment or not, from the requirements of system grounding...
 
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