Synchronizing Inverters
Okay, I give up. What is E-11 and who is the regulatory body?
Funny, I can't imagine why 2 power sources cannot feed the switchboard.
When I worked aboard a tanker we always paralleled gensets to when offloading
product.
Regards,
John
One of the main issues is that E-11 does not permit two power sources
connected
to load at the same time.
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John said: "... Okay, I give up. What is E-11 and who is the regulatory
body?
Funny, I can't imagine why 2 power sources cannot feed the switchboard...."
My understanding is that "E-11" is referring to a section of the ABYC
electrical code. The ABYC has no regulatory standing. That said, they are
recognized experts in the field of marine electricity. If there is an
electrical fire, and blame is being established, the ABYC regulations will
be taken into account by the insurance company, and the judge, in assessing
blame. So, in other words, the ABYC regulations aren't technically a "law"
but they are critical to comply with. (my understanding anyway...)
Here is a link to the E-11 standard:
http://www.abycinc.org/committees/.%5CE-11.pdf
My guess is that the section that was being referred to is 11.5.3.7, which
says:
"11.5.3.7. Individual circuits shall not be capable
of being energized by more than one source of
electrical power at a time. Each shore power inlet,
generator, or inverter is a separate source of electrical
power."
My sense is that technology has moved faster than the rules.
As was mentioned earlier in this thread, there are inverters which have sine
wave matching capability, allowing them to supplement the power coming from
batteries with the output from a generator (such as the Victron Multi-plus -
http://www.victronenergy.com/inverters-chargers/multiplus-12v-24v-48v-800va-
3kva/). Although, technically, the Multiplus may be legal according to
11.5.3.7. The boat is still being powered by a single inverter, but the
inverter is merging both AC and DC input. I haven't found it in E-11, but
I'm sure there is a carve-out for devices which have as their primary
purpose the merging of multiple power sources into a single output.
There's another point of confusion with my interpretation of 11.5.3.7, which
has to do with multiple inverters. For instance, many boats have two 110
inverters. These can be combined to get 240 output. In this instance two
inverters represent ONE source of electrical power, and could be argued to
conflict with 11.5.3.7.
I'm no expert on E-11, so no promises that the above is accurate... Form
your own opinion.
-Ken Williams
Nordhavn 68, Sans Souci
Ken Williams wrote:
Here is a link to the E-11 standard:
http://www.abycinc.org/committees/.%5CE-11.pdf
My guess is that the section that was being referred to is 11.5.3.7, which
says:
"11.5.3.7. Individual circuits shall not be capable
of being energized by more than one source of
electrical power at a time. Each shore power inlet,
generator, or inverter is a separate source of electrical
power."
REPLY
In order to make sense of ABYC standards you have to understand the
context in which they developed. The original intent of what is now
11.5.3.7 was to prevent boats from plugging into two dock outlets at the
same time while combining the feed internally in the boat. Many marinas
are fed from transformers with either two 120V legs or three legs from a 3
phase transformer. Combining two such legs will result in a dangerous
situation. It poses a danger of short circuits and fire.
As Ken says, the technology has moved ahead of regulations and standards.
This is always the case. Safety standards always lag developments. Often a
standard only gets promogulated after an accident reveals a dangerous
condition. We have shore power converters that can safely combine multiple
dock power outlets even with different voltage and phase relationships.
John is also correct that ship's can use multiple generators feeding the
switch board. ABYC was originally developed for small runabouts and
recreational craft. It was never intended to be a standard for large ship
construction. Yet many large yachts are more like ships than recreational
boats in their electrical systems. To fit the necessary droop controls
to a small genset is prohibitively expensive. I was informed by Alaska
Diesel that it was not cost effective on gensets under 25kW - 30kW sizes
As for Victron and other European products. Bear in mind that ABYC
technical commitees are staffed by people from the manufacturers and as
such they have the domestic industry's welfare in mind as much as they
consider the safety of the public. In some ways ABYC is a thinly disguised
form of restrictive trade practice. Why else prohibit the european
product designs which meet all relevant safety standards in Europe. Yes I
am aware of movement to harmonize CE and ABYC standards but the process
moves at a glacial pace.
Some of the builders of large yachts choose to apply the ABS (American
Bureau of Ships) standards rather than living with the restrictions
imposed by ABYC.
Perhaps the greatest irony is that synchronizing inverters in the form of
grid-tie has been accepted by UL and NEC for quite some time. So why not
allow it under ABYC provided the same safeguards are in place. After all
ABYC uses UL and NEC plus NFPA as their guidelines.