Article 480 Storage Batteries

Shazam

Member
Industrial environment installed wet-cell storage batteries in a series configuration with a nominal 540VDC. Doesn't artical 480.7 require a "split string" connection to seperate the batteries to keep the battery group nominal voltage below 250VDC? Manufacturer isn't addressing this article requirement and says series connection is acceptable. Battery disconnect has a diagram on the door which shows configuraiton for both series and split connection. photo.JPG
 

GoldDigger

Moderator
Staff member
Industrial environment installed wet-cell storage batteries in a series configuration with a nominal 540VDC. Doesn't artical 480.7 require a "split string" connection to seperate the batteries to keep the battery group nominal voltage below 250VDC? Manufacturer isn't addressing this article requirement and says series connection is acceptable. Battery disconnect has a diagram on the door which shows configuraiton for both series and split connection. View attachment 9416
Section 480.7 appears to apply to field constructed battery banks rather than manufactured assemblies, so I am not sure it applies to your situation.
If the internal design meets the separation requirements, then there is no problem with how the + and - leads are brought out to the load.

The two diagrams shown on the sticker seem to be conveying the important requirement that all three poles of the switch must be in series with the current path to safely open under load and withstand the applied DC voltage.
Whether you connect anything external to the middle pole of the disconnect seems to be almost irrelevant if there are only two terminals on the battery bank itself.
 

Smart $

Esteemed Member
Location
Ohio
No. 480.7 is about physical grouping and separation of live parts. In reality, you can place more than one group immediately adjacent to the next with no separation of battery cases as long as the live parts meets the insulation requirement for spacing.
 
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infinity

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Staff member
Location
New Jersey
Occupation
Journeyman Electrician
If I remember correctly the battery strings needs to be arranged so that their voltage does not exceed 250 volts in any one string.
 

Shazam

Member
If I remember correctly the battery strings needs to be arranged so that their voltage does not exceed 250 volts in any one string.
This is how I interpret the article. There is a lot of information to address from insulation, grouping and voltage. I am trying to maintain a literal interpretation. When the code says "Cells shall be installed in groups having a total nominal voltage of not over 250 volts." isn't this clearly saying the connected string can't exceed 250V? I am surprised that the industry doesn't have more information on this condition.
 

GoldDigger

Moderator
Staff member
This is how I interpret the article. There is a lot of information to address from insulation, grouping and voltage. I am trying to maintain a literal interpretation. When the code says "Cells shall be installed in groups having a total nominal voltage of not over 250 volts." isn't this clearly saying the connected string can't exceed 250V? I am surprised that the industry doesn't have more information on this condition.
Even if the group size is limited to 250 volts, I do not see any reason that the terminals of the group have to be separately brought outside the battery housing. You could just make the jumper connection between them internal to the storage system as long as the terminal air gap distance was maintained. Insulated wires do not count as exposed parts.
So what you really have is either one string of 500 volts or two strings of 250 volts in series, depending on how you want to look at it. :)
 

ron

Senior Member
This is how I interpret the article. There is a lot of information to address from insulation, grouping and voltage. I am trying to maintain a literal interpretation. When the code says "Cells shall be installed in groups having a total nominal voltage of not over 250 volts." isn't this clearly saying the connected string can't exceed 250V? I am surprised that the industry doesn't have more information on this condition.
Literal interpretation would be that there is at least 2" of air (insulation) between the shelves of a cabinet breaking the groups into segments <250V. So split string disconnects are not required.

BTW The 2014 NEC eliminates the equivalent of 480.7 (the numbers change), so there is only special requirements if the string is <250V. I guess they figure if it is >250V it is being installed with some engineering supervision. Maybe the reason is in the ROC/ROP's
 

GoldDigger

Moderator
Staff member
Literal interpretation would be that there is at least 2" of air (insulation) between the shelves of a cabinet breaking the groups into segments <250V. So split string disconnects are not required.
The wording in 2011:
Insulation, which can be air, shall be provided between groups and shall have a minimum separation between live battery parts of opposite polarity of 50 mm (2 in.) for battery voltages not exceeding 600 volts.
If the shelves are made of an insulating material, I do not even see this are requiring the shelves to be separated, just the batteries on the shelves. And the two inch limit specifically applies to live battery parts. The size of the air gap or sheet insulation between other parts of the batteries, like non-metallic cases, is not specified.

If you want to look at design rather than regulation, you would need to consider creep length along surfaces (which may be wet with battery acid spray) as well as the size of the air gap, if that is what is used.
 
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