VFD wiring cable Requirement

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Usually a shielded cable is recommended when you put the input and output conductors in the same raceway.
 
Not a NEC requirement but have seen where they installed a prefabricated shielded cable inside of a newspaper inserting machine that were on VFD'S. Large 5 million square foot hospital/ research center/ a.but key cars building probably had over 500 drives. Most drives were within 50' of old plan Jane NEMA frame motors. Never had trouble using THWN wire to feed these motors. Newest 12 story building had 18 pulse drives for all motors 40 HP & larger except for soft start o. 250 HP Fire Pumo. Older installed drives had plain Jane line reactors on incoming power and newer installs have can not remember the name but line filters that had contactkrs, capacitors etc.
 
VFD cable is a scam. Belsen among others should be sued for false advertising. It is that bad. Allen Bradley has repeatedly told customers they must install VFD cable to fix issues with bearing fluting and reflected waves, then claim it’s an installation problem or a motor problem or some other lie to cover for the fact that the VFD cable did nothing to address the problem.
 
paulengr said:
VFD cable is a scam. Belsen among others should be sued for false advertising. It is that bad. Allen Bradley has repeatedly told customers they must install VFD cable to fix issues with bearing fluting and reflected waves, then claim it’s an installation problem or a motor problem or some other lie to cover for the fact that the VFD cable did nothing to address the problem.
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We had special Allen Bradley drives designed just for newspaper printing presses to most of the time act as a brake to maintain pressure on paper. While at the A&B class on these drives was told it took 10 man years to program. All of these 15HP motors were feed with common THWN. building wire with no problems. A&B never said anything about using overpriced special shielded cable.
 
brother said:
I was informed that the new NEC requires special cable/wiring for VFD's. I have seen the manfacturer instructions that require it, but not the NEC. Can someone please help me locate the NEC requirement?
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I think if you read carefully the manufacturers instructions don't actually require it. It is merely a suggestion. It is not a code requirement.
 
paulengr said:
VFD cable is a scam. Belsen among others should be sued for false advertising. It is that bad. Allen Bradley has repeatedly told customers they must install VFD cable to fix issues with bearing fluting and reflected waves, then claim it’s an installation problem or a motor problem or some other lie to cover for the fact that the VFD cable did nothing to address the problem.
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I don't think it is quite to the level of scam, but it is overhyped as a solution to what are non-existent problems in most applications.

In any case from what I can see, most people don't install it properly anyway.
 
petersonra said:
I don't think it is quite to the level of scam, but it is overhyped as a solution to what are non-existent problems in most applications.

In any case from what I can see, most people don't install it properly anyway.
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If I tell my customer the solution to their problem is putting in a ridiculously overpriced cable and I make the claims that Belden and AB do, it’s at best misrepresentation and at worst fraud, depending on whether or not you can prove intent. Regardless I don’t have the advantage of a virtual monopoly on selling certain products.

VFD cable can solve:
1. Multiple motor cables in the same wire way coming from different VFDs that cause reflected wave damage due to mutual coupling (shielded cables only). So will ANY shielded cable.
2 issues caused by poor assymetrical capacitive coupling again due to poor cable installation. Not a property of the cable itself but rather fixing poor installation.
3. Fixing grounding issues if the manufacturers instructions are not followed. Again nothing special here, just fixing installation.
4. Issues with surge rating of #14 THHN (not THHN-2) only (#12 or larger no advantage) when exposed to wet conditions with cable length over 100-200 feet and motor is surge rated over 1500 V. Yeah it’s a very tiny special case.

5. It cannot act as a filter to block high frequency EDM type bearing fluting.
6. It can’t block common mode VFD induced currents causing bearing fluting.
7. It cannot do anything to prevent reflected wave damage to the motor and as established except for one very minor exception it is no more surge resistant than THHN/THWN.

Yet ALL of these are precisely what Belden and AB claim. At best items 1-3 are misleading but legal. I challenge anyone to find a case 4 in the wild. And cases 5-7 are outright misrepresentation. Plus they charge roughly 400% of the market price for what amounts to 2 kV foil wrapped cable and the profit motive is the clear case for fraud which is the “intentional misrepresentation of a material fact for the purposes of material gain”. If it’s not outright fraud I don’t know what is.

As a motor shop tech I get called on to clean these things up all the time. I go in and take measurements and shoe what the problem is. If I can solve it with magic cable I will. I’m still waiting for that day to come.
 
paulengr said:
Plus they charge roughly 400% of the market price for what amounts to 2 kV foil wrapped cable and the profit motive is the clear case for fraud which is the “intentional misrepresentation of a material fact for the purposes of material gain”. If it’s not outright fraud I don’t know what is.
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I thought it was basically swa cable with foil shield.
 
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