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Old 09-14-2007, 08:18 PM   #16
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Hot Tub Install--Grounding Rod Question


Rob,..
1)The sketch is not correct. That ground rod at the spa poses a significant hazard if a voltage gradient were to be present.
1a)I sure hope you ran these conductors in rigid conduit or PVC, not direct burial UF cable or conductors in EMT.
2)You are getting licensed, experienced personnel to give YOU the CORRECT answers, not your dad. He does not need to, nor does he have the expertise, critique the responses.
3)One thing appears to be missing. The #8 SOLID Cu bonding conductor. This is probably the most important aspect of this project. All metallic components of the spa and the motor must be BONDED together in on CONTINUOUS UNBROKEN loop with the proper lug type fasteners.
4)I really suggest getting a permit from your local inspection authority, and while you are there....talk with him on the bonding/grounding aspect of this project...not your dad. He may mean well ... but he's wrong.
Good Luck .....

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Old 09-15-2007, 03:59 AM   #17
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Hot Tub Install--Grounding Rod Question


Rob:

One question before I drown you with information....What kind of surface is the spa set on concrete...wood or other surface?

First I want to say that adding a ground rod to the spa panel is not a requirement and in my opinion will not add safety to the spa as your Dad seems to feel. But on further inquiry I was in error that it would be a code violation. There is a rather obscure code section that does allow the ground rod in a supplementary application as you are showing it in your diagram. I verified this as being acceptable on another professional forum but with several reservations from those electricians. The general argument for using a ground rod in the application you show in your diagram is Section 250.54 of the NEC, it permits a grounding electrode to be connected to an equipment grounding conductor, as described in 250.118. Essentially, this allows for localized earthing to hold the equipment ground to the same value as the local ground nearby that equipment. This "supplementary" ground rod is not considered part of the electrical service grounding electrode system.

But it is not to be considered a ground fault path to clear electrical faults causing the overcurrent device (circuit breaker) to open.

This is why your Dad is mistaken, fault current will not flow to the spa ground rod you show in your diagram from an electrical short in the spa equipment, it flows on the equipment ground ran with the branch circuit conductors and spa panel feeder back to the power source.

So please read the below explanations to your questions.

Quote:
I don't quite understand the part about "having to use a dedicated GEC to bond the rods, not the EGC from the spa feed."
GEC.....Grounding Electrode Conductor.

EGC.....Equipment Grounding Conductor

The above acronyms are completely different systems... ground rods are part of the GES (grounding electrode system) in which all electrodes are connected to the main service panel and each other using a gec (grounding electrode conductor). This conductor is usually a #6 awg bare copper conductor. The GES is not a grounding (earthing) for the electrical system to provide safety from ground fault..... it is for property protection from a high voltage event like lightning or a huge power surge coming from the utility. It serves no benefit of human safety for your spa.

The EGC (equipment ground) is for human safety and facilitates the bonding of metal parts to an effective ground fault path back to the center tap of the separately derived system (Transformer) to allow sufficient current to flow to trip a breaker. Fault current does not flow to earth via the grounding electrode conductor to the ground rods. It flows back to the source. The earth is is not a good enough conductor to allow current to flow with the necessary amps at normal residential voltages to get a circuit breaker to trip out. The ground electrode system (GES) is not the equipment ground system (EGC).



Quote:
Are you saying that this plan is improper (dangerous)?
No.... if done properly it is not a hazard but creates a catch 22 IMO. NEC 250.54 allows the ground rod connected to the spa panel ground bar as a supplementary electrode (as you show in your diagram) for voltage gradient control. A supplementary ground rod is not subject to the grounding electrode bonding requirements of the main panel GES. So long as you connect it to the egc at the spa panel with a minimun #8 solid copper bonding jumper. However, this is rarely done and is not a requirement. It sets up a possibility of a voltage gradient energizing your spa metal via the equipment ground if the feeder equipment ground would open or be disconnected. So it's sort of a trade off. IMO I would drive it below grade and not use it as I think the installation is safer without it. It is more important that the metal of the spa itself has the proper bonding as Jgarth mentioned. This bonding requirement may or may not require any action on your part. It is this bonding of metal parts that is the most beneficial in eliminating an unwanted voltage gradient.... the ground rod is redundant in that it just adds more metal to be bonded.
When you have equal potential created by bonding the metal parts of the spa then by definition you do not have a voltage difference. Without a voltage difference, there can be no current flow. So you use an equipotential bonding system — not a grounding system..ie (ground rods) — to reduce shock hazards.

One of the myths about grounding (earthing) is that it reduces shock hazards by bringing everything to ground potential. Because the earth is not of uniform conductivity this will not be the desired result.

Some spas are self-contained in that all the spa equipment is inside the spa structure but the equipment is not on a common metal frame and therefore requires a 8 awg solid copper bonding conductor to be ran to all the metal parts.

Some spas are "packaged" in that all the equipment that runs the spa is mounted on a common metal frame and that frame serves as the bonding requirement so no further action by you is necessary.

OK...now to your diagram. First there are no positives just hot wires (ungrounded conductors) , neutrals, grounded legs, and equipment grounds.


As for the connections at the spa panel. See the diagram at the last of this post.. Your gfci doesn't have a ground wire .... it has a white neutral wire curly pigtail. It connects to the neutral bar of the spa panel not the ground bar. The neutral and equipment ground are separated at the spa panel. You may or may not have to carry the neutral to the spa control panel it just depends if the spa requires 120 volts along with 240 volts. The bottom right conduit shows the load side wiring going to the spa control panel.

I just can't cover eveything you need to know. So I'll just say that it is imperative that you have your spa inspected by the local codes department electrical inspectors to insure the safety of your family. They should also have a guide available for the requirements of a spa/hot tub install.

Some things you should read and credits for information provided.

http://www.mikeholt.com/files/PDF/Pooldownload.pdf

http://www.imsasafety.org/journal/novdec04/6.pdf

http://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/Grounding-versus-Bonding-Part-6-of-12~20050407.php


Stubbie



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Last edited by Stubbie; 09-15-2007 at 02:12 PM.
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