OR Room

[Hoyt]

I have 2 new OR rooms each with a duplex isolation panel serving 120 volt loads. Critical EM and Normal.

Each room has a 208v receptacle for a portable laser. I have a seperate isolation panel to serve this receptacle.... can this panel serve both OR room laser receptacles...even if the panel is located in one of the two rooms?

Thanks.

 

[shamsdebout]

Typically the vendor for any OR equipment will furnish a room layout, I designed a job and I restricted the panel to serve loads in that space. I don't have a code refence but the room layout I was furnished had seperate panels for each room, I assume that to be good design practice.

 

[Hoyt]

I agree it is good practice, I am just looking for if it is required. All 120v loads are circuit to the local room iso panel (which is only 120v sec.) The 3rd iso panel specifically installed for the laser receptacle(s) is going to feed both OR rooms.

 

[Hoyt]

I think I got it. 517.160(4)(b)(1)

 

[VUGear]

Yes, the 208V laser receptacles in multiple ORs are typically all served from a central isolated power panel.

 

[dbuckley]

Does the 208V supply have leakage detectors? If so, with a central leakage detector and remote recepticals the capacitive coupling in the cables may be enough to put the leakage detector into alarm.

 

[iwire]

Does the 208V supply have leakage detectors? If so, with a central leakage detector and remote receptacles the capacitive coupling in the cables may be enough to put the leakage detector into alarm.

That is a darn good point that should be considered.

Roger has posted some great engineering info for these systems and long runs are problematic. Another heads up is not to use THWN/THHN conductors as they have high leakage currents as opposed to XHHW.

 

[Karl H]

Another heads up is not to use THWN/THHN conductors as they have high leakage currents as opposed to XHHW.

I'd like to learn more about this. Does anyone have the archived post name
where Roger explains this?

 

[iwire]

I'd like to learn more about this. Does anyone have the archived post name where Roger explains this?

I could not find the thread but this may get you rolling

C. System Wiring and Conduit
The selection of a proper conductor is one of the most important design criteria of an isolated power
system. If improper conductor insulation is chosen, the result is the same as if the capacitive leakage is
raised. A good commercially available wire insulation for this application is cross-linked polyethylene,
having a mineral filler instead of a carbon black filler. A minimum wall thickness of 2/64-in. should be
demanded for use in 120 V, 208 V, and 240 V applications. It is also important to specify wire with a
dielectric constant of 3.5 or less, as recommended by the NEC and NFPA No. 99.
Standard Type THHN wire is definitely unsuitable. It can, however, be used for the ground conductor.
The code demands that the #1 conductor in the system be color-coded orange, the #2 conductor
color-coded brown, and the ground conductor color-coded green. In three-phase systems, the third
conductor shall be color-coded yellow.
Schneider Electric is often asked to specify manufacturers and wire catalog numbers for the low leakage
conductor. This is extremely difficult to do since the availability of these wires differs from region to
region. Also, manufacturers have sometimes discontinued production of wire types that we have
recommended. The most accessible XLP wire has been low leakage wire #FR-XLP (VW-1 XHHW-2).
Recently, manufactures have rescinded their notation in their specs for XHHW and XHHW-2. This note
referred to the recommendation found in the NEC (517-160) concerning the 3.5 dielectric strength. The
different compounds used in the manufacturing of the insulation have changed or are subject to
change, and the 3.5 dielectric strength may not be obtained. The XHHW and XHHW-2 insulation is still
the choice since it comes closest to meeting the recommendation. This is important to note since this
could affect the overall installation of an isolated power system.
Avoid the use of wire pulling compound since it increases the capacitive coupling. The code no longer
allows wire pulling compound to be used in conduits for isolated power systems. This compound is
usually unnecessary, because most of the runs on an isolated system are short. Occasionally, difficulty
occurs in circuits feeding portable equipment since these conductors are somewhat larger. These
difficult runs can be anticipated and provided for by using oversized conduits to ease the situation.
Obviously, conduits must be dry or the leakage characteristics designed into the system will suffer.
During construction, keep conduit ends capped so they remain free from moisture. The specifications
should state that, if moisture accidentally enters the conduits, they must be swabbed and thoroughly
dried before conductors are pulled. Use minimum fills for conduits; this results in a better random lay of
the conductors within the conduit, which further reduces the capacitive coupling.
The table below shows the approximate expected hazard currents per foot of power conductor, using the
various wiring schemes described in the preceding paragraphs.The consulting engineer can use this
table to estimate the system hazard current at the design stages. Values given are approximate;
variations in humidity, conduit moisture content, conduit fill, and wire insulation will give different results.

From page 20 if this pdf http://stevenengineering.com/tech_support/PDFs/45HIPS.pdf

 

[roger]

Another heads up is not to use THWN/THHN conductors as they have high leakage currents as opposed to XHHW.

I'd like to learn more about this. Does anyone have the archived post name
where Roger explains this?

Here is an excerpt from a SQ D white paper on Isolation Power Systems.

Use cable with the best insulation possible. The insulation on the cable should have a dielectric constant of 3.5 or less and, in this regard, all XHHW wire is not created equal. Square D recommends Rome Cable brand, catalog number VW-1 XHHW-2 Spec 2110 because it seems to consistently give the best results. The particular wire you are using may be listed as having a dielectric constant of less than 3.5, but wire manufacturers generally do not list an absolute dielectric constant. So you don?t know if the wire?s dielectric constant is 3.49 or 2.49. Wire insulation types THHN, THHW, THW, THWN and TW are not suitable for use on isolated power systems.

Do not use wire pulling lubricant of any kind on the branch circuits. Wire pulling lubricants tend to change the dielectric of the insulation. If in doubt about the ability to pull-in the conductors, use a larger conduit. The insulation on XHHW wire is thicker than THHN and not as slippery. So plan ahead and ask you distributor for some wire samples.

I do not have the whole document right now but I'll try to post it later, I do have it at work, I think.

Roger

 

[Karl H]

Thank you Bob, this is very good information.

 

[Karl H]

Thanks Roger!

I have heard of pulling soap changing the conductors dielectric but, I just
dismissed it as myth such as "I read it in the code book somewhere"
excuse. Now I'm really digging deeper into the research and finding some surprising information.