While many people mistakenly use the terms interchangeably, BONDING and GROUNDING are two very different things, with very different purposes. Again, bonding and grounding are DIFFERENT. HEY, they're even spelled differently. The very simple explanation of bonding is that it is done to prevent you from being shocked/electrocuted when your left hand touches one metal component, and your right hand touches another metal component. By running a wire (bonding wire) from one metal component to another, stray electricity (from a short for example) will equalize through the wire and one metal component will NOT have a greater voltage in it than another metal component. Grounding on the other hand is to give stray electrical current a place to go, other than through you. To some extent, the two work in conjunction with each other, sort of as backups for each other. BUT THEY ARE SEPERATE and DIFFERENT.
So why the confusion? One reason may be due to the use of grounding rods, which when installed correctly, have a bare copper wire attached to them (wire used for bonding is required to be bare copper wire). This wire looks exactly the same as a bonding wire. However, the only place grounding through a grounding rod should be done is at the main electrical panel (that's main panel, not sub panel). The reason a main electrical panel is grounded through a grounding rod is to limit the voltage imposed on the entire electrical system by lightning, unintentional contact with higher-voltage lines, or line surges. Besides the grounding rod, the panel needs to also be grounded back into the electrical providers "grid".
Additionally, grounding through a grounding rod has its limitations. Grounding (earthing) of electrical equipment doesn't provide a low-impedance fault-current path to clear ground faults (translation: "lower" voltages don't travel well, or freely, through the surface of the earth). In fact, according to the NEC, code prohibits the use of the earth (a grounding rod) as the sole return path because it's a poor conductor of current at voltage levels below 600V [250.4(A)(5) and 250.45(B)(4)]. In reality what this could do is potentially electrify the ground around the spa and has the potential of ELECTROCUTING you. If you were to be standing on the ground and touch something that IS properly grounded you could be fatally electrocuted (electricity in the electrified ground travels up through you and out to what your touching, which is properly grounded). There's actually a documented case of this happen at a fish farm in the UK. The little fishies were periodically being electrocuted from an improperly grounded/bonded power line TWO MILES AWAY.
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