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Home > Archive > Electrical code Compliance > June 2005 > msg - secondary winding earthed
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| Author |
msg - secondary winding earthed
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| Hi guys,
I have a 3phase without neutral dishwasher supplied at 440V, internally
there is a transformer accros two phases to stepdown the voltage from
440V to 230V, well the electrician earthed one pole of secondary
winding (230V side) directly to the protectional earth and metallic
frame.
What's the reason of this wiring?
Do you think that according EN60335-1 is permitted? I mean according
the definition there is a direct contact between LIVE PART and
ACCESIBLE METAL PART!!
Obviously I'm talking about a class I equipment.
----
Thanks in advance maz.
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| "maz" <alternative.mail@gmail.com> wrote in message
news:1111648591.880281.210580@f14g2000cwb.googlegroups.com...
quote:
> Hi guys,
> I have a 3phase without neutral dishwasher supplied at 440V, internally
> there is a transformer accros two phases to stepdown the voltage from
> 440V to 230V, well the electrician earthed one pole of secondary
> winding (230V side) directly to the protectional earth and metallic
> frame.
> What's the reason of this wiring?
> Do you think that according EN60335-1 is permitted? I mean according
> the definition there is a direct contact between LIVE PART and
> ACCESIBLE METAL PART!!
> Obviously I'm talking about a class I equipment.
You should ask your electrician.
Are you sure transformer is 220 and not 120v?
Either way, if it had no reference to ground, it would really, really be a
hazard.
As for your 440v, if you are in the US, it is most likely that your 440v has
a connection to ground thru a wye type neutral that you cannot see. The
frame of the dishwasher should be solidly grounded via a code-described
ground path. Any phase to ground fault in this scheme is limited to 277v
and will trip the 440 (480) breaker.
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| Grounding one point on the secondary creates a ground reference for the
secondary. Else one side could short to the 440 supply and the other
side would be higher than 440 to ground reference.
In the US, if the transformer is part of the dishwasher its use would be
covered by the listing for the dishwasher (like UL). If the transformer
is added by the electrician, the secondary is a "separately derived
system" and in general (without looking it up) has to be grounded and
have a grounding electrode (like ground rod).
Bud--
"maz" <alternative.mail@gmail.com> wrote in message
quote:
>Hi guys,
>I have a 3phase without neutral dishwasher supplied at 440V, internally
>there is a transformer accros two phases to stepdown the voltage from
>440V to 230V, well the electrician earthed one pole of secondary
>winding (230V side) directly to the protectional earth and metallic
>frame.
>What's the reason of this wiring?
>Do you think that according EN60335-1 is permitted? I mean according
>the definition there is a direct contact between LIVE PART and
>ACCESIBLE METAL PART!!
>Obviously I'm talking about a class I equipment.
>
>
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| phil-news-nospam@ipal.net 2005-06-17, 11:30 pm |
| On Tue, 29 Mar 2005 14:03:33 -0600 Bud <BudNews@isp.com> wrote:
| Grounding one point on the secondary creates a ground reference for the
| secondary. Else one side could short to the 440 supply and the other
| side would be higher than 440 to ground reference.
|
| In the US, if the transformer is part of the dishwasher its use would be
| covered by the listing for the dishwasher (like UL). If the transformer
| is added by the electrician, the secondary is a "separately derived
| system" and in general (without looking it up) has to be grounded and
| have a grounding electrode (like ground rod).
That depends on where the transformer is. Connecting it to the grounding
wire in the supply circuit is sufficient. Note that an autotransformer
does not make a separately derived system, but an isolating transformer
does (or it can be wired as an autotransformer to avoid being treated as
a separately derived system if that is undesired).
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
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| |
| Andrew Thomas 2005-06-17, 11:30 pm |
| phil-news-nospam@ipal.net wrote:
quote:
> On Tue, 29 Mar 2005 14:03:33 -0600 Bud <BudNews@isp.com> wrote:
>
> | Grounding one point on the secondary creates a ground reference for the
> | secondary. Else one side could short to the 440 supply and the other
> | side would be higher than 440 to ground reference.
> |
> | In the US, if the transformer is part of the dishwasher its use would be
> | covered by the listing for the dishwasher (like UL). If the transformer
> | is added by the electrician, the secondary is a "separately derived
> | system" and in general (without looking it up) has to be grounded and
> | have a grounding electrode (like ground rod).
>
> That depends on where the transformer is. Connecting it to the grounding
> wire in the supply circuit is sufficient. Note that an autotransformer
> does not make a separately derived system, but an isolating transformer
> does (or it can be wired as an autotransformer to avoid being treated as
> a separately derived system if that is undesired).
>
Hmmm, I think the poster has reason to be concerned. If the 440-230
transformer is of the delta-delta type, and the diswasher is desigend
for delta power, I don't think any leg should be grounded. The case of
the transformer and the chassis of the dishwasher should be grounded.
Note I speak more from an engineering perspective than from an
electrician perspective, and not professionally in either respect. If I
were the poster, I'd look into it further: and not take the intalling
electrician's word for it. I'll probably know the answer myself within
a couple weeks: will be installing a rotary phase converter. I know the
frame of the converter will be grounded: but if I am to tie one of the
output phases (L3, obviously, as L1 and L2 are supplied by the utility)
to earth ground I will be STUNNED.
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