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本帖最后由 xmlhifi 于 2013-8-7 22:25 编辑
国标86型墙插面板一般都是塑料外壳的,地线直接接到汇流排上,属于单点接地方式,这样地线上的干扰噪声比较低。
相比之下,如果按美标墙插施工,用金属底盒+金属套线管,用于普通美标插座的地线与外壳是相连的,外壳与底盒套线管都接到建筑公共大地上,地线又单独铜线接到地线汇流排上,这样实际上形成了多重接地 即环地,容易受到公共地线上的电流干扰。
为了解决美标电源墙插的干扰问题,HUBBEL提出了地线绝缘的产品,明显降低了地线干扰。对比如图所示:
常规美标墙插
常规美标墙插,环地干扰大。
HUBBEL地线绝缘墙插
HUBBEL地线绝缘墙插,采用一点接地,干扰减小。
引用HUBBEL原文如下:
Hubbell Isolated Ground Receptacles
Why do you need an isolated ground device?
When mounting a conventional receptacle in a steel box, the ground
is commonly established through the existing electrical system . This
is done by using either the grounding clip on the receptacle’s
mounting strap, or by running a ground wire (which is part of the
“normal” existing system) to the green grounding screw .
In a conventional receptacle the grounding contacts are connected to
the mounting strap and the green grounding screw . Thus, even when
a separate green wire is brought to the receptacle, it is still tied into
the normal ground . This occurs since the mounting strap is in contact
with the box grounding system, therefore, a “pure” isolated path to the
ground is not established .
The Problem
The conventional grounding receptacle provides safety for personnel
and equipment . However, the ground network also serves as a giant
antenna and conductor of electrical noise . This electrical noise is
electromagnetic interference and is caused by numerous transient
ground currents . This can produce random transient electrical signals
on the grounding system .
As a result, sensitive electronic equipment such as point of purchase
terminals, accounting machines, computers and highly sensitive
medical and communications equipment, can pick up these transient
signals . This can interfere with the proper operation of the equipment .
The Solution
The isolated ground receptacle is similar to a conventional receptacle
except for one important change . Insulating barrier construction, first
patented by Hubbell, isolates the ground contacts from the mounting
strap . The green grounding screw is connected directly to the grounding
contacts . The isolated equipment grounding circuit is completed by
running an isolated ground wire to the green grounding screw . This
ground wire passes through intermediate panel boards without being
connected to their grounding terminal and terminates directly at an
equipment grounding conductor terminal of the derived system or
service, in accordance with NEC® requirements .
The Result
This “isolated ground” can be kept relatively free of electrical noise .
This is achieved since the grounding network has less branches, fewer
sources of noise, and is connected to the ground at a single point . |
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