Question:
Also are
modern units usually internally bonded or does bonding have to be done by
the electrician/installer?
Answer:
The grounding and bonding are two entirely different systems with different
purposes.
Grounding for a hot tub is the same as grounding for any other appliance
(with special requirements for added reliability). The purpose of grounding
is to establish a ground reference for conductive metal enclosures and to
provide a return path for ground fault currents.
Bonding refers to the practice of connecting together all metal parts of the
pool, and nearby fittings, piping, metal conduit, and so on to eliminate
any possible voltage gradients in the pool (hot tub) structure or
differences among metal objects that can be touched by a person in the pool
(hot tub).
Newer approved packaged hot tubs will be manufactured with bonding already
in place for all the hot tub equipment. It will be up to you to bond to the
bonding block inside the hot tub all metal conduits, piping, and large
metal parts (usually taken to mean greater than 4 ins. in diameter) within
5 feet horizontally and 12 feet vertically from the water's edge or
surface. The rules are the same as for swimming pools, and the 12-foot
height seems a bit excessive to me, unless your hot tub has a diving board,
but that is the rule.
The bonding and grounding systems should be connected together at exactly
and only one point. Newer hot tubs are provided with a bonding block (often
labeled "ground") for this purpose. The block is usually located in or
attached to the control unit inside the hot tub. Occasionally there are two
blocks, one for the electrical ground and one for bonding, and they will be
connected together.
Bonding requirements are covered in 2002 NEC section 680.26, which I
recommend reading if there are any nearby metal objects.
