NEMA Enclosures Questions and Variable Frequency Drives
NEMA Enclosures Questions and Variable Frequency Drives
(OP)
I am the Owner rep. that recently inaugurated an ocean front resort in the Caribbean. The resort has a mechanical building that has two chillers, heat exchange system and three boilers to supply chilled and hot water to 21 buildings. On that same building we have ten Variable Frequency Drives with NEMA 1 Enclosures. The mechanical systems have been working for a year and so far we have five VFDs failures. The manufacturer claims that NEMA 1 is an unacceptable choice of enclosure because the building is non conditioned and is less than a mile from the sea. The contractors claim that NEMA 1 is an acceptable enclosure as long as is used in doors. Do you have an experience with VFD's failures and Nema 1 enclosures? Are Nema 1 enclosures industry standard in mechanical spaces? Suggestions and comments are welcome






RE: NEMA Enclosures Questions and Variable Frequency Drives
What does failure mean? What happens? Shuts down? Blows up? Shorts out? Component failures?
If components failing/shorting humidity and condensation may be a factor. But you need to describe the failures better.
Rafiq Bulsara
http://www.srengineersct.com
RE: NEMA Enclosures Questions and Variable Frequency Drives
We place a call to factory and they indicated that NEMA 12 drives should have been used in the mechanical areas because NEMA 1 enclosures don't offer adequate protection.
Response: two types of failure one that the drive completely shuts down and there is no way to power it back and the second is drive is showing the following fault message: HF28 Power stage thermistor 2 fault. In the manual the diagnosis is: Hardware fault – return drive to supplier.
RE: NEMA Enclosures Questions and Variable Frequency Drives
NEMA 12 does not necessarily provide protection against corrosion but its gasketed covers may help ingress of water or oil if that is the issue. I am not sure if it could prevent ingress of humidity and airborne salt though.
Your best bet may be to use NEMA 12 enclosure and air-conditions the space just to dehumidify it. Or use space heaters in the drive enclosures when drives are not active. Ask the mfr it they have such an option. Some combination of the above should solve the issue, if it is indeed due to corrosion as described.
Rafiq Bulsara
http://www.srengineersct.com
RE: NEMA Enclosures Questions and Variable Frequency Drives
Rafiq Bulsara
http://www.srengineersct.com
RE: NEMA Enclosures Questions and Variable Frequency Drives
"Indoors" in a tropical area is something less than absolute in my experience. Yes, VFDs in close proximity to salt spray air will corrode and deteriorate very rapidly. I have had that happen may times in sewage pump stations that are near beaches. Even if indoors in air conditioned spaces, there just is no way to keep out 100% of the salt spray when your VFD is sucking in hundreds or even thousands of CFM through the vents with blowers.
I was just at one yesterday at a water intake fish screen facility in central California, 100+ miles from the ocean. The VFD was in a sealed stainless steel enclosure with an air conditioner, the installation is about 8 years old. The VFD was fine, but they have gone through 3 air conditioners in 8 years. There just is no way out of corrosion problems with gear exposed to weather.
NEMA 12 would definitely help, but you also need anti-condensation heaters with thermostats to keep the enclosure temperature above the dew point. Keep in mind that the dew point in 90% humidity can be very high! There are also some anti-corrosion emitters that out gas a vapor which helps to prevent corrosion. Hoffman sells them here in the US, I don't know if they actually make them or not however. but neither of these strategies will help if the enclosure is not sealed, and if it is sealed, it will need air conditioning. You can, by the way, get stainless steel air conditioners.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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RE: NEMA Enclosures Questions and Variable Frequency Drives
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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RE: NEMA Enclosures Questions and Variable Frequency Drives
I spoke to a nearby hotel management and they indeed have a substantial amount of VFD's failures, but their failures were in a period of two years and not in one year. The only common denominator has been NEMA 1 enclosures.
Regarding your observations about the enclosure I have spoke to several consultants and most of them agree that NEMA 12 in a high humidity environment next to the ocean would not work. They mentioned that the VFD's must have a NEMA 4x enclosure with control temperature and humidity. But the factory insists that the NEMA 12 drives will solve the problem which for me does not make sense since my understanding is that NEMA 12 does not protect against a corrosive environment.
Any experiences with NEMA 12 or NEMA 4x enclosures?
I have enclosed the full diagnostic report and some pictures send by factory
RE: NEMA Enclosures Questions and Variable Frequency Drives
RE: NEMA Enclosures Questions and Variable Frequency Drives
NEMA 12 and NEMA 4X will do an approximately equal job of keeping air exchange to the outside in check as long as they're gasketed and conduit entries are sealed. The big difference is that the NEMA 4X enclosure is corrosion-resistant itself, while the NEMA 12 is probably just painted steel.
In other words, either will help your situation if you control temperature and humidity inside the enclosure I think. The NEMA 12 version might begin to corrode itself, though.
Make sense?
Good on ya,
Goober Dave
RE: NEMA Enclosures Questions and Variable Frequency Drives
Rafiq Bulsara
http://www.srengineersct.com
RE: NEMA Enclosures Questions and Variable Frequency Drives
RE: NEMA Enclosures Questions and Variable Frequency Drives
Yes, I have used the Commander drives. Nothing in particular wrong with them, I just recognized the fault code.
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RE: NEMA Enclosures Questions and Variable Frequency Drives
What is the voltage and approximate HP rating of these drives?
Keith Cress
kcress - http://www.flaminsystems.com
RE: NEMA Enclosures Questions and Variable Frequency Drives
RE: NEMA Enclosures Questions and Variable Frequency Drives
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: NEMA Enclosures Questions and Variable Frequency Drives
For this reason, anti condensation heaters are typically run at 50% voltage and without thermostats. An occasional issue is locating a heater with a low enough rating. (It doesn't take much heat to stay above the dew point.)
50% voltage drops the wattage to 25%. This may be an advantage when selecting a heater, along with long life.
Bill
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