I have a spa that is a true 240 vac,I have it wired to a 2 pole 30 amp gfci in a subpanel. The red(L1) goes to one load on the breaker and the black(L2) goes to the other load connection on the breaker. The load neutral of the breaker is vacant.The white pigtail on the breaker is attached to the insulated bus bar. The green ground coming from the spa is connected to the grounded bus in the subpanel. All is fine when the heater is not on,but when the heater comes on there is 64 volts when I take measure from the spa water to the earth. If the heater is delivering the voltage why doesn't the breaker trip? How is the heater putting voltage to the water? The heater is heating the water. The spa is obviously not being used.Thanks, Chris

Not enough info.

How old is the spa heater?
How old is the GFCI?

Have you taken a resistance reading between either leg of the heater element and ground? (With the power off of course).

Also, a DMM can pick up 64 volts right out of thin air given the right circumstances.

The heater is in a sweewater austin 1999. I found the problem by standing on the wet grass and touching the water when the heater was on. Not a nice surprise.
The breaker is a new Murray.
I have not taken any readings between the heater terminals yet.
Chris

Do you have a 'Wiggy' style voltage tester that you can use? (Electro-mechanical meter).

no, just digital.
I know the voltage is present because it shocked me.
Chris

My first point in this is to go after the GFCI. (Fix heater is priority 2). Either it's not hooked up correctly (somehow?) or it's faulty. I have zero experience with Murray brand GFI's so right now I can trust yours about as far as I could throw it.

I was asking the question because that's the quickest (and safest) way to do an outside test on a GFCI, using a wiggy volt meter. One probe on any leg of the gfci (or either power lead at the control), and touch the other to ground - it should trip.

Of course this isn't a minimum current level test, but it'll at least give you an indication of operability with an outside imposed ground fault. If you have a reasonable appreciation of electrical safety, a 5 watt 4.7k resistor to ground is a good test too.

I take it the test button works on this gfci?
And you only have one circuit breaker going to this tub?

This is what I have found, the last guy who worked on the spa replaced the heater and did not use the straps or any other method of grounding the heater. The heater had no connection to any bonding or grounding. The element must have failed introducing the voltage to the water. I attached a jumper from the heater case to a bonding lug on the spa panel and as soon as the heater fired the breaker tripped. This heater has no mounting studs and MUST be grounded.
Thanks, Chris