480 volt tranformers on prodution floor? - in compliance on not?

Status
Not open for further replies.
G

gpmainteng

Member
I have just started in a new position with a manufacturing company with aprox. 90 machines on a production floor. All of these machines are fed from a overhead bus system. A portion of these machines require a transformer; the transformers are installed at the corner of each machine on a wooden pallet. I will note that there are no guards in place and this is a forklift trafic area. The feed for these transformers come from a disconnect on the 480 bus and a 15 foot SO cord directly into the primary of the transformer. The secondary is flex into the machine, and each machine has it's own means of disconnection. In addition the transformer is bonded to a driven ground rod through the concrete floor. one problem they were facing was the building is not capable of supporting the transformers from the ceiling.

I am questioning the installation of the transformer on the pallet, What basic requirement must be followed for transformers in a production area? what about the the lack of guarding and point of disconnection?

~matt
 
gpmainteng said:
I have just started in a new position with a manufacturing company with aprox. 90 machines on a production floor. All of these machines are fed from a overhead bus system. A portion of these machines require a transformer; the transformers are installed at the corner of each machine on a wooden pallet. I will note that there are no guards in place and this is a forklift trafic area. The feed for these transformers come from a disconnect on the 480 bus and a 15 foot SO cord directly into the primary of the transformer. The secondary is flex into the machine, and each machine has it's own means of disconnection. In addition the transformer is bonded to a driven ground rod through the concrete floor. one problem they were facing was the building is not capable of supporting the transformers from the ceiling.

I am questioning the installation of the transformer on the pallet, What basic requirement must be followed for transformers in a production area? what about the the lack of guarding and point of disconnection?

~matt
Click to expand...

I don't have a problem with most of it.

Are you concerned that the fork lift drivers might accidentally pickup a pallet with a transformer on it?

The driven rod sounds like it might be an issue though. Is the secondary of the transformer grounded to this rod? This is OK if it is also grounded to the closest grounding electrode (probably the building steel) if this is an SDS.
 
A question and a statement.

First I would like to know, If a transformer serves just the one machine does it fall in the definition of a separately derived system, or is it just an integral part of the machine, and not part of the premises wiring?

I ask because we have many of these where I work also. They are not bonded to the GES. Most are used to convert European voltages to US voltages. Grounding is done via the ECG for the circuit sometimes with sometimes without a ground rod.

Second. I know from where I work that the NEC is not the only code that must be complied with in this situation. Other safety codes may require guarding, lines painted delineating the zone for traffic from the zone for equipment, width of travel routes depending on the type of traffic (fork lift, mule train, foot) etc.
 
1. See 110.26
(B) Prevent Physical Damage. In locations where electric equipment is likely to be exposed to physical damage, enclosures or guards shall be so arranged and of such strength as to prevent such damage.
2. Also if the transformer is not part of the machine, then it may need a connection to a grounding electrode system, per 250.30. May as this depends on the secondary voltage configuration. Also it may require a system bonding jumper, again depending on the voltage. The transformer requires primary and secondary overcurrent production.
The SO may not be compliant, it has to have a cord connector. The rules for SO cord are in Art 400.
I commonly hear about industrial and manufacturing facilites that tend to ignore the NEC, because they feel they are exempt. Many do not have qualifed electricians, get permits or inspections.
 
tom baker said:
I commonly hear about industrial and manufacturing facilites that tend to ignore the NEC, because they feel they are exempt. Many do not have qualifed electricians, get permits or inspections.
Click to expand...

Thanks Tom. I am trying to learn here.

I did have to laugh at your statement because the plant I was talking about is a federal government installation. They ARE exempt from the NEC. At least when it is their engineering dept who draws the planns. For bid work, "follow state and local codes" is in the spec.

I have noticed that for most installatoins the systems are engineered over and above the NEC. So while they are not required to follow it, they do, and then some.

Since the machies I am refering to are purchased as an assembly, I am wondering if that fact that the transfomer is a seperate component from the machine even matters. I would see this as not being part of the building wireing and therefore not covered by the NEC, the same way the internal parts of your toaster are not covered.
 
Even if you call the transformers part of the "equipment wiring" and say it doesn't have to be grounded, I'm pretty sure that once you drive a ground rod and connect it, then you have to bond it to the building's grounding system. You can't have separate grounding systems without bonding them together.
 
re: transformers

re: transformers

The transformers are not OEM supplied, they are to step down 480 to 208/230. They are only feeding one machine. Does this qualify as a seperatly derived system?





jbwhite said:
A question and a statement.


First I would like to know, If a transformer serves just the one machine does it fall in the definition of a separately derived system, or is it just an integral part of the machine, and not part of the premises wiring?

I ask because we have many of these where I work also. They are not bonded to the GES. Most are used to convert European voltages to US voltages. Grounding is done via the ECG for the circuit sometimes with sometimes without a ground rod.

Second. I know from where I work that the NEC is not the only code that must be complied with in this situation. Other safety codes may require guarding, lines painted delineating the zone for traffic from the zone for equipment, width of travel routes depending on the type of traffic (fork lift, mule train, foot) etc.
Click to expand...
 
gpmainteng said:
The transformers are not OEM supplied, they are to step down 480 to 208/230. They are only feeding one machine. Does this qualify as a separately derived system?
Click to expand...

I'd be inclined toward the idea that the premises wiring extends to the point at which the power is connected to the machine. that would be downstream of the transformer.
 
steve66 said:
Even if you call the transformers part of the "equipment wiring" and say it doesn't have to be grounded, I'm pretty sure that once you drive a ground rod and connect it, then you have to bond it to the building's grounding system. You can't have separate grounding systems without bonding them together.
Click to expand...

I agree, but we can bond, in this case to the ECG for the circuit, and not have to bond to the building GEC.
 
petersonra said:
I'd be inclined toward the idea that the premises wiring extends to the point at which the power is connected to the machine. that would be downstream of the transformer.
Click to expand...
I would agree with this if the transformers are not OEM. But if they are, then I would differ.
 
Federal government installations are exempt from the Nec ??
I have heard that, but only with anecdotal evidence.
I, too, work at Federal sites, and the only people who claim that they are exempt are those, for example, who say we don't need an EPO system in the computer room.
I have never seen any official documentation to support that claim.
Somebody will need to convince me
thanks
db
 
I would think that without bonding to the building steel, you could create a situation for injury due to inappropriate step or touch potentials. It may be unlikely, but nevertheless a possibility.
 
How is the possibility any differnt in either situation.

First the TX is a seperate box sitting next to an eqiptment.

Second the Tx is installed in the equiptment.

Either way we are talking OEM tx or OEM certified tx.

I still believe that this falls under equipment, and is no longer covered in the NEC because it is not a part of the building wiring.
 
Transformer OCP and grounding observations

Transformer OCP and grounding observations

Hi there.
450.3 (B) allows for primary-only OCP of a transformer operating at under 600 volts nominal. Assuming that this machine is a large enough load to justify a pallet-mounted transformer (9+ amp primary), the OCPD may be sized at 125% of the primary FLA, or the next standard OCPD rating above that.

I figure that the ground rod driven into the concrete had better be tied to the building GES, according to 250.50 and 250.52(A)(5). This code requirement was clarified in the 2005 code iteration.

Whether the transformer was supplied by the machine manufacturer or not, the obligation to NEC compliance should include the transformer. My belief is that the machine probably has a main disconnnect and/or OCPD to which the transformer secondary is connected. Article 409 covers from that disconnect on, but even 409.3 says that transformers in industrial control panels are governed by article 450. Therefore, I disagree with jbwhite and recommend primary OCP according to 450.3(B) and grounding according to 450.10 (which, oddly enough, refers to article 250... hmmm)

Regards,
Dan
 
Status
Not open for further replies.
Top