Your questions answered: How to design an electrical room with a reduced footprint

In this Q&A, the Schneider Electric expert discusses how electrical room components can be reduced to allow for flexibility and value

By Brandt Smith July 7, 2022
Courtesy: Schneider Electric

Electrical engineers are often challenged to design electrical rooms that not only meets codes and standards, but that is also designed to fit in increasingly compact spaces. In such projects, electrical engineers are tasked with coming up with designs that utilize small-sized components without compromising performance, reliability and the ever-increasing need to be efficient and sustainable.

During the June 16, 2022, webcast, “How to design an electrical room with a reduced footprint,” the presenter covered a variety of topics. Unanswered questions are addressed here.

Read responses below from Brandt Smith, Power Systems eMobility Leader, Schneider Electric.

What is CPT?

A CPT is a control power transformer. This is used to supply control power to the switchgear in some applications.

How much space might be saved by using an equipment line-up versus separate equipment for a typical 200A, 480/277V panelboard, 75kVA stepdown transformer and 208/120V panelboard?

Depending on the number of circuits the footprint of an INEQ transformer combo can cut required space including fallback area less than half. Even with larger circuit counts sidecar MPS panels offer full height availability of our largest interiors. Remember hanging a transformer from the ceiling or sidewall significantly raises install labor which more than offsets $/ft. savings. Only key design factor is to get your prelim study completed before manufacturing. Releasing INEQ product before ID-ing inadequate breakers can cause issues with any required post-release changes.

What is the approximate lead time for some of the integrated equipment or gas and solid insulated equipment? What can we do if we design a room around that and then find we can’t get it within the project schedule?

GIS equipment is currently approximately 28 weeks, but may vary depending on the lead time of certain selections, such as relays. Integrated Equipment Lead time today is 16 weeks but we should start recovering standard lead times (six weeks) by January 2023.

What are the advantages of the metal clad switchgear if any? If Gas insulated switchgear is a superior product what drives the demand for meta clad?

Instead of saying one is better than the other, I would rather say they are based on different design philosophies. Both are good tools to be used to solve power system challenges. GIS/SSIS is based on the concept that we can engineer most failures out of the equipment. An example of this is withdrawable breaker. Withdrawable breakers are a major failure point so we use fixed mounted breakers to remove the failure point. Metal clad switchgear is based on rapid recovery of loads in case of failure. Instead of superior engineering, we replace a failed breaker with a spare.

Is the 2sis NEMA 3r or is it just for indoor use?

It is NEMA1 but we do offer NEMA3R solutions.

Usually, space saving equipment is more expensive and normally does not get the approval of the procurement person who is not interested in lifetime cost. How do we get past that?

It sometimes is more expensive. For example:

  • GIS (reduced footprint) costs less and air insulated switchgear
  • HVLcc (reduced footprint) typically costs less than traditional fusible disconnects
  • SSIS switchgear (reduced footprint) is comparable to metal clad switchgear

When the reduced footprint version costs more, the key is to look at overall costs. For example, if the floorspace costs $500/sf, use that cost savings to justify the equipment.

What is the break point on size of transformer to consider hanging where structural wall/ceiling support will need specific design to address supporting means?

Negative net value to hang 300kVA and below versus INEQ transformer combo due to installation costs.

Are the GIS and/or 2SIS have been used to any HCAI (OSHPD) related projects?

Neither GIS nor PremSeT have been used for HCAI (OSHPD) so far. PremSet currently has OSHPD certification, but renewal will depend on if there is commercial interest. The most recent communications from West sales area team were that there are no opportunities in the pipeline that would require it.

As an IEC global product, GHA has not been certified to local requirements, but does meet the following:

Synthetic seismic tests – highest requirements:

  • waveform acc. to IEEE 693-2005 2) and STUK Guide YVL 2.6 3)
  • 5x S1- OBE = 0.5g (Operating basis earthquake)
  • 1x S2 – SSE = 1g (Safe shutdown earthquake)

Uniform Building Code (UBC):

Classification UBC seismic zone 4 (highest in the U.S.)

What about solid insulated gear?

No gas is used with SSIS switchgear. SSIS switchgear uses epoxy for the dielectric.

Are this integrated equipment approved for use in NYC?

NYC Yes – we have multiple projects in NYC that use integrated equipment. Macy’s Herald Square is full of integrated gear so just visit the Miracle on 34st

What % of MV switchgear do you see being specified as Arc Resistant vs non-arc resistant?

Roughly 5% in my area (PNW)

What gas is used in your GIS? I know SF6 is trying to be phased out.

SF6 is used in all GIS. It is being phased out but there are no designs in the market at this time. Schneider Electric is developing a design that replaces SF6 with air but it isn’t released yet.

Any cons of using wireless devices/components?

Some clients are worried about cybersecurity and will not permit digital wireless control

How does the cost of 2SIS switchgear compare with GIS?

SSIS is 5kV and 15kV rated. GIS is rarely used below 27kV.

Is GIS Switchgear a smaller footprint than 2SIS switchgear

SSIS is 5kV and 15kV rated. GIS is rarely used below 27kV.

Outdoors, what is realistic maximum summer temperature, including transformers, we are seeing 110°F.

Standard transformers are designed for a 30 average / 40 Max (104°F) We can design for a 40/50 (122°F Max) but that has to be designed at time of order.

A variety of electrical systems can be reduced in size. Courtesy: Schneider Electric

I’ve used GIS in power and industrial plants. If this gear is used inside of a residential or commercial building or a ship engine room, are there any concerns regarding the SF6 (or replacement insulating gases) being discharged into the occupied spaces? Any gas detection needed? Also, in case of fire exposure, would it require overpressure protection vented to outdoors like refrigeration machines?

The amount of SF6 gas used in MV switchgear is minimal and doesn’t typically represent a danger. That being said, I recommend checking with applicable regulations and standards.

As for overpressure protection, there are blow out devices on the SF6 tank.

For GIS the customer MUST understand cable entry and separation, typically at the bottom and the need for a cable entry vault below the GIS

The cable requirements depend on the manufacturer. One manufacturer requires space below the GIS for cable entry and to replace a breaker in case of failure. Schneider Electric’s design does not require a cable vault.

With California SF 6 being discontinued within three years by the CARB State Agency will this equipment still stay small or will it increase room size if it can’t be used

The equipment replacing GIS will have the same footprint

present project, using integrated transformer panels.

There are over 1,000 projects using integrated gear this year: Federal, Banking, Health Care, Retail, EV Charging, Microgrid, Chip Fabrication, Automotive, Oil & Gas, Food and Beverage… If there is a specific application you would like to see an example for, please provide those details.

Can we get a transformer with integrated primary disconnect and secondary overcurrent protection?

There is the Model III offer that has an HVL/HVLcc and LV line integrated into one solution. Product is managed by Smyrna. VPI transformer included. Up to 1000 KVA max. Great compact solution.

We can also offer a Liquid filled pad mount with a LBOR 2-3 or 4 position switch, primary fusing and install a secondary breaker up to 2500 Amps in the LV compartment.

Does SF6 still have approval issues because of greenhouse gas issues?

This depends on the site location. Some locations like California are more restrictive. Most location have no issues with SF6 equipment.

Why not ALL COMPACT or REDUCED PRINT equipment become standard?

This isn’t a one size fits all situation. Sometimes the full-sized equipment is better for our customers.

How is MV cable termination space incorporated into compact GIS or SSIS equipment? Do you typically need to allow provisions for cable trenches for bottom entry into this equipment to allow the clearance for the terminator length? What about your HVLcc fused switchgear (bottom entry)?

Unfortunately, given the current supply chain and transportation constraints that are evolving every day, we have to closely monitor every project timeline. However, our commercial and manufacturing teams work diligently with you to find the best solution in each case.

I have 120 Electrical Meters @ 208V required on an Apartment high-rise. Want to use 20 – 6-meter stacks. These stacks are to be located on various floors so need disconnects in Main Electrical room. Should we use a Switch board for the isolation switches so I can work on a stack. Who can help me design the equipment to minimize the Elec Room size?

Use 6-Mains rule on a switchboard to orient feeders to each meter array. House power feed may be read via utility dedicated external CT cabinet. In some jurisdictions a utility compartment w/i the switchboard may be needed for house power to be metered separately. If high-rise extends beyond 7 floors a busway feed with local bus plugs to each array may be more cost effective.

You mentioned that you’ve seen many occasions where large-frame breakers have been used when smaller MCCB’s could be used. I believe this is primarily to address potential changes that may be necessary for selective coordination. Does Schneider Electric consider this when making recommendations for smaller gear?

We do offer Mission Critical Breakers in smaller frame sizes that help with Selective Coordination and offer the ability to provide a smaller footprint.

What is the expected life of an E-house?

With proper maintenance, the external structure of an e-house will outlast the equipment inside.

Do e-houses meet Canadian electrical code and standards? Are they manufactured in Canada?

Yes, the meet Canadian codes. SE does have partners in Canada that can manufacture e-house.

is QED-6 considered a switchboard?

Yes, QED6 is the switchboard counterpart to our metal clad switchgear.

Does Schneider make retrofit l-v panels……..i.e., guts customized to fit in an existing can?

Yes, Schneider Electric can support the use of existing enclosures, although the interior is manufactured as standard, only the trim is custom manufactured. It is up to the contractor on how best to mount the interior into the existing tub.

Is liquid cooling being added?

Yes, SE is partnering with liquid cooling vendors in all architectures, Direct to Chip & Immersion.

Are the transformers instigated in the switchboards?

Yes, sort of. We use a switchboard structure that will close couple as a UL listed system with our QED2 switchboards. But we build these assemblies in a different factory. Since they bolt together and connect via power cable, they can ship separately to the job site to be coupled in the field if sold in conjunction with a larger amperage switchboard.

Can you perform a thermography on a front access switchboard?

You can, but I would recommend using continuous thermal monitoring. IR scanning only detects issues at the time of testing where continuous thermal monitoring is testing 24/7.