[reefburnaby]

Hi,

I think I have been asked this question about ten times now....I am too lazy to open the CSA standards book to look up what exact is required. [img]images/smiles/icon_smile.gif[/img] The book is somewhere in my company's library...I'll see if I can get the official word.

I guess the main concern is how to protect us from getting electricute in any event. To get electricuted, you must have about 18 to 40 milliamps of electrical current flowing through your body. Suppose, we have a powerhead that is leaking currents because its protective epoxy shell is cracked. Let's consider these cases.

1. 2 prong PH

The stray currents will flow through from the PH, into the water. So, if your fingers touch the water, then the currents will flow through your fingers and your body.

2. 2 prong PH with ground probe.

As in case 2, the power will flow out of the PH and into the water. However, the stray currents will flow to the ground probe...even if you touch the water. This is because, the connectivity between the water and ground is better with the probe than it is for your body. Since electricity is lazy...it takes the easy way out. [img]images/smiles/icon_smile.gif[/img]

3. 3 prong PH (with or without ground probe).

The 3rd prong on a PH is usually attached around the iron core of the motor. A motor consists of a magnet(i.e. the impeller), an electromagnet (i.e. the iron core with magnetic wire wrapped around it). If the epoxy cracks, the iron core and the magnetic coil will be expose to the water. Since the core is grounded, this will help draw any stray currents from the motor to the ground. However, when the epoxy is not cracked, the tank water is not grounded. Hence, the 3 prong gives the user extra protection.

2 prongs with same prong width.

For motors, it is usually okay since it only affects the direction at which the motor will spin.

Hope that helps.

- Victor.

[ 01 January 2002: Message edited by: reefburnaby ]