ECN Forum Forums General Topics of the Trade General Discussion Area opinions on project

Hello folks, I have a project I have been asked to llok at and am not quite sure how to go about it. Thought I would throw it out here for opinions.

Multi story hotel. Just opened within past 4months. So my loads from power co are lacking the electrical baseboard heat in all the guest rooms. Aug load was 104Kw in a 15 minute period. At 208/120v 3phase thats is around 300amps.

The service disconnect rating is 2500a. 65' from electrical room exterior door is our primary fed padmount.

Eight 3.5" PVC conduit runs go from padmount to bottom of switchgear. There are eight sets of what looks like 250Kcmil conductors, but I am guessing they are probably 350's for the 2500a rating.

Oh, the customer wants a back up generator for building.

I would like to dig up conduit bank, and install outdoor transfer switch on new pad next to new generator. No room in electrical room for switch.

1st, how could I manage to keep hotel operational without interuption (hotel is full capacity for next five years).

I need to cut into duct bank to either pull conductors out of xfmr, or pull out of gear. Transformer would be easier for one, because genny pad would be right next to xfmr pad.

Other concern, the xfmr pad sits in between the back of the building and a large hill. No retaining wall and in that grass area is a underground drain. When I looked at the building the grass was a marsh from all the rain.

Thoughts or questions?

If you were here in NJ, I would tell you that you need plans/spec from a NJ Lic PE/EE/Architect first.

Whatever you do, a shut down will be required for the POCO feeds. If the hotel is 'booked' for 5 years, that is a problem, right?

Installation of a new pad mount xfr (with POCO blessing), and set-up of the gen & transfer equipment, and feeders into the existing electric room...may be a thought.

Scott35 may have some ideas!

You are not going to run without an interruption but you might be able to do it with a minimum interruption if you staged everything and had everyone necessary there for the cut over. It will be a little more expensive that way because you will usually end up with extra wiring but with some thought you should be able to do it.
The obvious time is 4AM but if you end up with alarms going off that may not be as attractive

Where is the power company metering? You need to be on the load side of the current transformers with your transfer switch.

If your ATS is going to be ahead of the Main, you'll need to have an ATS that's rated "Suitable as Service Equipment".

Also carefully watch your system grounding.

You will definitely need an outage in order to do the tie-ins; how about seeing when the hotel could best tolerate it.
I would think that the majority of the guests would be out of the hotel after 10:00 in the morning and the power would need to be back on by early afternoon to give the HVAC a chance to catch up with the stale air before everyone comes back for the evening.

Do everything that you possibly can before you shut down; and you will be a real hero to the hotel if you can get the power restored before your scheduled deadline. If you figure that your crew will need a 3 hour shutdown, tell the hotel that they will be down for no more than 4 hours and prepare to receive their accolades when you get back online an hour early. I would recommend that you use extra crews if you need to in order to minimize the total downtime.

Something else to consider:

Currently the conductors from the padmount are probably the property of the PoCo and being such they are most likely undersized for the building service.

As such you can't simply place a padmount ATS next to the transformer, reroute the service conductors to the ATS and provide new conductors from the ATS to the transformer since the service conductors would now be the property of the hotel. You will have to provide new 400's in each of those existing 3.5" conduits (350's wouldn't be code compliant).

For practicality you're going to have to rent a generator large enough to carry the hotel through the process. These rigs are to be found in Thom Cat or on the web.

While on the generator-set the biggest loads would be eliminated. That is: you'd schedule for good weather and lock out the air conditioning load, etc.

By using a hefty gen-set you've taken the monkey off your back. The Poco pulls the fuses and records the CT readings... While you un-bus their secondaries...

Then you swing into final action with what ever scheme the EE's have come up with. At this scale, my AHJ won't permit an EC to perform the design. So I never sweat it.

With all of the design work and permits -- this project will come together next Spring, at best.

The idea of swinging this project without massive temp power -- doesn't fly with me.

BTW, consider a back-fed tap onto the mains, also. You might be able to rent/ use a second-hand breaker for such a scheme.

This will also have to be co-ordinated with Life Safety issues.

Comm service secondary conductors/conduits here (NJ) are customer installed & owned. Customer also installs primary conduit/ducts & POCO installs and owns the primary side. PS territory, the EC makes the secondary terminations, supplies the lugs & hardware, at the padmount. Responsibilities vary by POCOs, and areas.

The Life-Safety issues can pose additional obstacles, which should be discussed with the local AHJs (Fire Marshal) As this is a new building that probably has fire sprinklers, does it have a fire pump?

Was any mention of the genset size?? Wish to run the whole 2500 amp existing service loads? If you tie-in the existing life-safety the gen becomes 'legally required' as opposed to 'optional'; if there is a Fire Pump, that's another obstacle. Were any preperations 'made' for a 'future generator'?? You mention it is only 4 months old! Definite PE/EE/Architect required.

350kcmil THHN 90 deg C is 350amps x 8 conductors is 2800 amps. Service is 2500

No engineer or architect is required in this municipality. All they require is an inspection. I have already spoke with township and poco. (this is not PECO or PPL or MetED) I also met with a engineer for the poco, to meet me at the xfmr to open it it up for me to look at. I am though, considering getting an electrical engineer involved just for the liability.

The life Safety is something I had not considered. THanks for bringing it up.

As far as disconnecting secondaries from gear and back feeding with temp genny, that was my thought process as well. We will be trying to convince the owner this needs to be done next spring. No A/C or heat would be on.