>> http://www.allegromicro.com/en/Products/Part_Numbers/0754/index.asp
>>
>> So you just stick the large straight leads on the IC into any old
>> ferrite core suppressor
>
>The ferrite is in the package

I don't think they have any ferrite in th package. It is not needed.

>> Or does this actually wire inline in the AC circuit being sensed?
>
>Yes, in-line
>
>> I thought these type of sensors were non contact

You may also like to look at a similar device made by LEM, which I learnt 
about just before finding out about the Allegro Microsystems ones.

See 
http://www.lem.com/hq/en/component/option,com_catalog/task,displayserie/serie,FHS%2040-P--SP600/output_type,/ 
(watch out for URL folding, try http://www.lem.com/ otherwise) for their 
Minisens range. These require an external loop around the sensor to achieve 
the same as the Allegro units, but it does mean that you can vary the 
sensitivity, while still using the same device, by varying the number of 
turns around it. 

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