Well Studying for my masters I came across a question that asks " what is the minimum clearance from a transformer to a concrete wall?" They have the answer stated as 3'. My question is did they get this from 110.32 work space about equipment? In transformers 450.3 I can not find anything about 3' clearance. Am I looking in the wrong area or does this fall in the 110.32 area?
transformer clearances
- Thread starter Dano2
- Start date
Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
Is that the exact wording from the question?
450.3 - is transformer overcurrent protection and would not have a space requirement from a concrete wall.
110.32 - is for over 1000V and the wording of the question would provide additional insight as to if this is the correct section to be referencing.
Within 450 and other sections of the code, there are various requirements that might require a set back from a concrete wall. For starters, 450.9 - ventilation.
While you might need a working space (110.32 is for over 1000V), that doesn't always apply to the back of a transformer unless you need to access that part for servicing.
450.3 - is transformer overcurrent protection and would not have a space requirement from a concrete wall.
110.32 - is for over 1000V and the wording of the question would provide additional insight as to if this is the correct section to be referencing.
Within 450 and other sections of the code, there are various requirements that might require a set back from a concrete wall. For starters, 450.9 - ventilation.
While you might need a working space (110.32 is for over 1000V), that doesn't always apply to the back of a transformer unless you need to access that part for servicing.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
There must be more to the question.
Is this a dry type ventilated transformer?
Is it an oil-filled padmount next to a concrete building with windows?
Is rear access required for servicing live parts?
Is this a dry type ventilated transformer?
Is it an oil-filled padmount next to a concrete building with windows?
Is rear access required for servicing live parts?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
If the answer is 3' then who knows what they meant. If they're asking for working space, (which it sounds like with the answer of 3') then you would need to know the voltage. For 208-480 the distance would be 42". Some will argue that working space does not apply to a transformer.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I am one of those.
Most dry type transformers are fully accessible from the front only, while others may have ventilating fans in the rear. Liquid filled units typically have no accessible parts in the rear at all. Manufacturer supplied mounting brackets for transformers provide no rear working space at all.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Me too. I’ve had several arguments over the years about transformer clearances and the need for “servicing” from the rear. I have honestly never seen a transformer in a room with clear space all around it (other than trapeze mounted I guess), it’s always front access clearance space only.
I’ve had end users who are trying to squeeze stuff into closets try to argue that you don’t even really need front access clearance for transformers because access is not required for “servicing while energized”, but I don’t take it that far. Testing is a form of “servicing” in my book.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I agree most transformers do not require rear access or side access for that matter but I believe that the OP's question is pertaining to the front given the answer was 3' for a concrete wall.
I apologize. The full question was, What does the clearance have to be from the front of a transformer to a concrete wall in front of it?
- Location
- Illinois
- Occupation
- retired electrician
Do you agree that the 110.26(A) working spaces apply to the front of the transformer?
- Location
- Illinois
- Occupation
- retired electrician
In that case you also need to know the voltage as the required condition 2 workspace can be 36", 42", or 48" based on the voltage. If they had not said concrete, then in might have been a condition 1 installation and the answer is 36" for all voltage levels in Table 110.26(A)(1).
One of the facilities I work in recently changed their policies so that you basically never can open energized equipment thats over 300V, I recently realized its to reduce places where 110.26 was being applied for working space like transformers.
- Location
- Illinois
- Occupation
- retired electrician
If I am the inspector, that would not change my enforcement of 110.26(A). Rules are always broken.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
You need to know the voltage to maximum ground.
Yeah I was confused as to why new safety rules picked 300V, I posted about it a while back.
Its a large facility, but space is in short supply so they had some ongoing issues with an AHJ over clear working space and yellow tape on the floors got removed, the $$$ attorneys up at corporate were successful in arguing that
"the electrical safety policy of XYZ is equipment operating over 300V shall not require examination, adjustment, servicing, or maintenance while energized"
" due to corporate policy disallowing any such examination, adjustment, servicing, or maintenance while energized it is our opinion 110.26(A) only applies to XZ designated areas on the plans"
(It still applies infront of switchgear and panelboards, but not transformers and other equipment.)
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
It all depends.
But in general no. Really small transformers cannot be opened at all, except for their wiring compartment. Very few locations perform any maintenance at all on ventilated transformer below 150kVA. So if 110.26(A) applies to all transformers, shouldn't it also apply to motor terminal boxes?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I tend to agree but don't transformer terminals get occasional IR scans requiring working space?
The thing I am learning about the NEC which is probably completely obvious to you guys is when you have something like 110.26 and it has main paragraphs (A) (B) (C) or in other articles they use (1) (2) (3) then each of those main paragraphs has sub paragraphs 1 2 3,
then if (A) does not apply nothing under (A) applies until you get to (B) and so on. Its easy to get lost in the weeds of the code only to find out the entire section I am in does not apply.
So all the sections under 110.26(A) fall apart if its not 'likely' that you'll need to examine that something energized.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Some do, but not many below 150kVA.
- Location
- Illinois
- Occupation
- retired electrician
Public Inputs 1088 and 1089 would have added the following to the parent text of 110.26(A).
The code making panel rejected both PIs with the following panel statement.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
They should have put the information from their comments directly in article 450.