Low Voltage Switchroom Design Guide

By Steven McFadyen on May 9th, 2012

Low voltage (LV) switchrooms are common across all industries and one of the more common spatial requirements which need to be designed into a project. Main LV switchrooms will typically contain free standing switchboards and Motor Control Centres (MCC), along with auxiliary equipment required for the room to function (bus ducts & cable containment, distribution boards, lighting, small power, air-conditioning equipment, fire fighting, etc.). In addition LV switchrooms often also house other related equipment – marshalling panels, UPS systems, control panels etc..

This article gives some design guidance for the correct sizing of these rooms.

Switchboards

In laying out the LV switchroom, actual switchboard dimensions should be used. Typical switchboard dimensions would be:

height would be 2.2 m (2000 mm for the switchboard and a 200 mm plinth)
width 600 mm to 1050 mm depending on construction
depth 600 mm
weight 200 to 400 kg per panel

Room Dimensions

Switchroom Clearances

Clearances around switchboards should comply to local regulations. In the absence of other guidelines the following minimums can be used:

Switchboards rear clearance
- 0 cm for front entry switchboard
- 75 cm for rear entry switchboard
Switchboard side clearance
- 100 cm for all switchboard
Switchboard front clearance
- 70 cm (150 cm preferred) for all switchboards
Vertical clearance above switchboard
- 400 mm (may require additional)

Design Considerations

access for personnel (normal and emergency)
access for equipment (installation, operation and maintenance)
regulatory compliance and approvals
cable containment and entries
earthing and grounding
water sealing (if below ground)
air conditioning, lighting & small power
fire detection, alarm and suppression

Environmental Category

Room climate is to IEC 60721-3-3

IR1 (indoor) - good heat insulation, air conditioned; office, shops, etc.
IR2 (indoor) - good heat insulation, air conditioned, heating/air conditioning may out of service for several days
IR3 (indoor) - no heat insulation, not air conditioned

Luxury Kipeto says:

5/27/2012 4:59 PM

Thanks for your website am based in Kigali Rwanda. For electrical wiring Rwanda is coming up.
- Steven says:
  
  5/27/2012 7:25 PM
  
  Thanks for the feedback Luxury. Glad you like the site.
dean says:

8/30/2012 9:20 AM

Hi,
Thank you for showing your site, it’s very useful. I have a LV switchboard, which has limited space as it’s built inside a 20ft shipping container. The information shows the distance from the front of the switchgear to the facing wall can be between 70 and 150 cm (150cm preferable). Can you advise please if this relates to a particular regulation? Thank you
- Steven says:
  
  9/11/2012 2:11 PM
  
  Different countries and supply authorities have different regulations. If the regulations at your location require a minimum distance you would need to provide at least this. If there are no regulations, from a good engineering you should not go below 70 cm - this would be my minimum even if regulations allowed for less. Ideally you would want people to be able to work/operate the switchboard in a safe environment; having 150 cm would give this.
Juan J. Isdray says:

11/15/2012 9:00 PM

Hi,

Thank for your information.

My question is related to environmental category, the point is how do you consider a switchtroom placed in subtropical ambient to power a fertilizer plant where explosive gas and vapor could be present or sorronding the switchrrom area.

Sould it be advisable to use aircondisionig or presurized method
Thanks in advance
Steven says:

11/16/2012 9:49 AM

If you have explosive gas present, you should be treating this as an hazardous area and selecting the appropriate equipment. Following post my give you some insight:

http://myelectrical.com/notes/entryid/126/hazardous-areas-iec-and-nec-cec-comparison

Pressurisation is an option in some instances, but it is only part of the solution and needs to be implemented in accordance with the hazardous area standard.

If your not familiar with area classification and installation in this type of environment, I would suggest you seek some specialist advise (or do a lot of research).
- Juan J. Isdray says:
  
  11/17/2012 10:10 AM
  
  Hello Mr Steven
  Thanks a lot for your attention to my question but, I made a mistake when express that the hazardous explosive gas were present in the switchroom when I would say that Hydrogen or propane gas could be surrounding (Not present)in the switchroom. Yes I am familiarizad with hazardous areas for several years working in a fertilizer plant, mainly the distribution transformer and switchroom in chemical plant are locate al least 20m far from such gas possible emission (Div II) areas.
  
  Summary: My doubt still is if pressurizing and isolating the cable trench entries at the room could be sufficient to prevent gas enter into switchroom. Sorry for so much annoying
- Steven says:
  
  11/17/2012 10:20 AM
  
  I would say the pressurisation is a viable approach. It's been a long time since I was involved in anything similar. If I was faced with this problem myself and considering pressurisation, I would be re-reading the standards and doing some research to get myself back up to speed.
  
  As extra thoughts - in addition to cable trenches, are there other openings where gas can enter. You may also consider other solutions - some type of sealing similar to Roxtec for example.
Juan J. Isdray says:

11/20/2012 8:16 PM

Hi Mr Steven
Here I am back again, yes there are some other entries to the switchroom througout cable trays but it is easy to seal with Roxtec, the big problem come from the cable trenches which has to be refilled with sand because trenches interconnect different areas and could transfer hazardous gases in between. So in absence of a relevant standard at my reach I am asking about your knowledg and experince in this matter.

Thanks so much in advance
Isdray
- Steven says:
  
  11/21/2012 2:06 PM
  
  Unfortunately I don't have access as well to the standards currently.
  
  If you decide on pressurisation, I think the key points are ensuring the air is not contaminated and obviously keeping the room at a positive pressure. In addition to pressurisation, you also have to option of providing enough air flow so the gas concentration in the room never gets above the lower explosive limit. If you implement either of these, then to get the details you need to read the standard (IEC 6009-13, IEC 6009-14).
  
  The easiest option is probably the sand (or some similar filling). If you can create a impermeable barrier to the gas you should be ok. If you do fill the trench with sand you may want to test the sealing before operation. If you have forced ventilation or air conditioning you may still want to set this to work at a positive pressure.
  
  If you want, you can also ask in the sites questions section and maybe some other users will chip in.
EE80 says:

4/21/2013 1:27 AM

Hi Steven,
thanks alot for your efforts.
How do you Configure number of breakers/ ratings per module?

thanks
- Steven says:
  
  4/21/2013 5:47 AM
  
  I would refer to the manufacturers technical information if I was trying to estimate. Most good manufacturers do have documentation allowing you to correctly select the number of breakers per module. Some manufacturers also have software to assist. Often the manufacturers themselves are also willing to do this for you.
  
  On the breaker ratings - I would also use catalogues and published technical documentation. If you search the site we also have some guidance on breaker ratings and I hope to post more in the future. Basically you need to select the appropriate frame size, trip unit and fault ratings. You should also consider that when installed in the panel, circuit breaker ratings may need to be derated (catalogues will be showing ratings for breakers in free air).
Sumit says:

5/13/2013 8:46 AM

Switchboard front clearance as70 cm (150 cm preferred) for all switchboards
Is there any IEC standard for this clearance.
Specifically I need a IEC standard for front clearance for non withdrawable type LV local panel.
- Steven says:
  
  5/13/2013 11:28 AM
  
  Thanks for the comment Sumit.
  
  I don't believe there is an IEC recommendation for this. If you do find one, please let me know as it would be very useful to myself as well.
  
  You need to at least allow the minimum for any local regulations you use. Personally I would try to achieve 150cm as this leaves space for people to move around with switchboard doors open and creates a safer work environment.
Pattabhiraman says:

5/15/2013 7:11 AM

Hi,

In Tamilnadu, India, we follow certain guidelines. When drawout type breakers are provided in panel, we allow atleast 2000mm front clearance. For Panels without drawout breakers, 1500mm front clearance should be good tradeoff between comfortable working and additional cost of space and infrastructure. The top clearance will be decided based on whether cabling is done above ground using cable trays. Clear space of atleast 600mm will be required for drawing of power cables in already laid cable trays.

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Low Voltage Switchroom Design Guide

Switchboards

Room Dimensions

Switchroom Clearances

Design Considerations

Environmental Category

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