Re: AC Voltage
¿ªÔÆÌåÓý
Thanks Buffalo John
for your good lesson, I learned news and refresh old knowledge that was lost.
With few words: Ground cable is important, and it have to be good.
/johannes
From: [email protected] <[email protected]> on behalf of BuffaloJohn <johndurbetaki@...>
Sent: Saturday, May 18, 2024 1:14 PM To: [email protected] <[email protected]> Subject: Re: [7x12MiniLathe] AC Voltage ?
See my answers below in red:
When in doubt, keep it simple, make sure your protection devices have all the proper connections to work, make sure your building wiring is strong enough to support your application (wiring size, breaker type and size, panel wiring,
panel balance, etc. etc. etc.), and when in doubt - ask.
On Sat, May 18, 2024 at 9:56?AM Johannes wrote:
Yes, getting a working ground is an important thing to fix.
Attaching to interior piping of a building was used in the past because that copper pipe ran outside into the actual ground. However, it is not a good way to make a ground connection because there are many ways it can be ineffective
or dangerous.And - you might not have a copper pipe going outside anymore. My son had his house repiped and the copper going outside was replaced with PEX.
What you need is to have the ground circuit actually connected to an EARTH return - which means a "ground" rod driven into the ground, near the electrical panel, with a heavy gauge wire connecting the rod to the panel. Grounds within
the building also need to be wired and not assumed to be connected by conduit.
Wild electricity is an interesting way to look at it!?
The purpose of the ground in these machine tools applications is to divert a live circuit to a safer place - ground. For example, suppose your motor overheats and the insulation is damaged. It is possible that the damaged insulation
lets the live power to the motor flow to the case of the motor. If someone were to touch the live circuit by touching the motor housing or something that is bolted to the motor and then also touch something that has a actual ground connection, it is possible
for current to flow between one touch to the other. If it is mains power, it can be lots of voltage and lots of current. While the fuse might blow when you become the bridge between hot and ground, more likely is that you would get a shock and worse - and
the fuse wouldn't blow.
A GFCI (Ground Fault Circuit Interrupter) breaker would have a better chance of stopping you from becoming the fusible link than a fuse.
An AFCI (Arc Fault Circuit Interrupter) breaker will also be useful when dealing with leakages as it can detect leakage from more than just ground.
Grounds don't make the AC more stable, they just make a return path for errant current. The quality of the AC coming in is governed by the power transformer that connects to the power company, the wiring along the way, balancing of
the loads, etc. While phases are referenced to ground, locally it might be different and this topic is a bit more than I want to tackle here.?
We had a case where a link in a meter corroded (really old meter, really old house (knob and tube in places still live), and something took out the circuit in such a way that the 240 coming in to the old house didn't have a neutral
reference that was solid One side had 40v and the other 200v. That was a power company call but a bunch of equipment was destroyed by the overvoltage situation (including a couple of MOV surge protectors).
Many MOV circuits are using the ground as the place to dump the transients. In practice, this can have unintended consequences if the ground return isn't really good. Power strips with cords and MOVs work only if the ground in the
building wiring is solid and not tied to neutral anywhere but where it is supposed to be. If the return path of the transient is weak, the the electricity will find a better path and that might be more problematic.?
Rule to follow - no extension cords on surge protecting power strips.?
Why? Because now you are hoping the ground connection on the power strip with a surge protector has a good ground connection and it it doesn't as it adds impedance to the circuit and that can make things worse (pulses decrease, but
pulse width lengthens).
Ground is a reference point. We call it ground because that is what was used
and is still used for many applications. In power circuits, it is useful to think of have a hot line, a return line, and a ground line. Inside electronic systems we also think of things the same way,
though we might refer to the ground of the system to actually be the return and an actual ground connection is used a different way.
-- Buffalo John |
Johannes